KUALA LUMPUR, Malaysia (AP) — Dozens of ships and aircraft have failed to find any piece of the missing Boeing 777 jet that vanished more than two days ago above waters south of Vietnam as investigators pursued "every angle" to explain its disappearance, including hijacking, Malaysia's civil aviation chief said Monday. 
 
 This photo provided by Laurent Errera taken Dec. 26, 2011, shows the Malaysia Airlines Boeing 777-200ER that disappeared from air traffic control screens Saturday, taking off from Roissy-Charles de Gaulle... (Associated Press) 
 
 A family member of passengers aboard a missing Malaysia Airlines plane wipes her tears at a hotel in Putrajaya, Malaysia, Monday, March 10, 2014. Vietnamese aircraft spotted what they suspected was one... (Associated Press) 
 
 A Chinese relative of passengers aboard a missing Malaysia Airlines plane looks out from a hotel room for relatives or friends of passengers aboard the missing airplane in Beijing, China Monday, March... (Associated Press) 
 
 This screengrab from flightradar24.com shows the last reported position of Malaysian Airlines flight MH370, Friday night March 7, 2014. The Boeing 777-200 carrying 239 people lost contact over the South... (Associated Press) 
 
 Malaysia's Department of Civil Aviation director general Azharuddin Abdul Rahman, right, speaks as Malaysia Airlines Group Chief Executive Ahmad Jauhari Yahyain listens during a press conference at a... (Associated Press) 
 
 Malaysian maritime officials found some oil slicks in the South China Sea and sent a sample to a lab to see if it came from the plane, the Department of Civil Aviation chief, Azharuddin Abdul Rahman, told a news conference. 
 
 Hundreds of distraught relatives were gathered in a hotel in Beijing, waiting to be flown to Malaysia. Of the 227 passengers, two-thirds were Chinese. There were also 38 passengers and 12 crew members from Malaysia, and others from elsewhere in Asia, Europe and North America, including three Americans. 
 
 "We accept God's will. Whether he is found alive or dead, we surrender to Allah," said Selamat Omar, a Malaysian whose 29-year-old son Mohamad Khairul Amri Selamat was heading to Beijing for a business trip. He said he was expecting a call from his son after the flight's scheduled arrival time at 6:30 a.m. Saturday. Instead he got a call from the airline to say the plane was missing. 
 
 Vietnamese ships working throughout the night could not find a rectangular object spotted Sunday afternoon that was thought to be one of the doors of a Malaysia Airlines passenger jet. 
 
 "We have not found anything that appears to be objects from the aircraft," Azharuddin said, adding that the search operation has involved 34 aircraft and 40 ships covering a 50-nautical mile radius from the point the plane vanished from radar screens early Saturday about one hour into a flight from Kuala Lumpur to Beijing. 
 
 He said officials from the U.S. Federal Aviation Administration and the U.S. National Safety Transportation Board have arrived to help in the investigation. 
 
 As hope faded for relatives of the 239 people who were aboard Flight MH370, attention focused on how two passengers managed to board the ill-fated aircraft using stolen passports. Interpol confirmed it knew about the stolen passports but said no authorities checked its vast databases on stolen documents before the jet departed 
 
 Warning that "only a handful of countries" routinely make such checks, Interpol secretary general Ronald Noble chided authorities for "waiting for a tragedy to put prudent security measures in place at borders and boarding gates." 
 
 Still, there was no indication that the two men had anything to do with the tragedy. 
 
 Possible causes of the apparent crash include an explosion, catastrophic engine failure, extreme turbulence, or pilot error or even suicide. 
 
 Azharuddin acknowledged many theories about the plane's disappearance, including hijacking. 
 
 "We are not discounting this. We are looking at every angle but again, we have to find concrete evidence," he said. 
 
 The baggage of five passengers who had checked in to the flight but did not board the plane were removed before it departed, he said. Airport security was strict according to international standards, surveillance has been done and the airport has been audited, he said. 
 
 On Saturday, the foreign ministries in Italy and Austria said the names of two citizens listed on the flight's manifest matched the names on two passports reported stolen in Thailand. 
 
 "I can confirm that we have the visuals of these two people on CCTV," Malaysian Transport Minister Hishammuddin Hussein said at a news conference late Sunday, adding that the footage was being examined. "We have intelligence agencies, both local and international, on board." 
 
 The thefts of the two passports — one belonging to Austrian Christian Kozel and the other to Luigi Maraldi of Italy — were entered into Interpol's database after they were stolen in Thailand in 2012 and last year, the police body said. 
 
 Electronic booking records show that one-way tickets with those names were issued Thursday from a travel agency in the beach resort of Pattaya in eastern Thailand. A person who answered the phone at the agency said she could not comment. 
 
 But no authorities in Malaysia or elsewhere checked the passports against the database of 40 million stolen or lost travel documents before the Malaysia Airlines plane took off. 
 
 A telephone operator on a China-based KLM hotline confirmed Sunday that passengers named Maraldi and Kozel had been booked on one-way tickets on the same KLM flight, flying from Beijing to Amsterdam on Saturday. Maraldi was to fly on to Copenhagen, Denmark, and Kozel to Frankfurt, Germany. She said the pair booked the tickets through China Southern Airlines. 
 
 As holders of EU passports with onward flights to Europe, the passengers would not have needed visas for China. 
 
 The Thai national police chief on Monday set up a task force to investigate the issue of the stolen passports. 
 
 Interpol said it and national investigators were working to determine the true identities of those who used the stolen passports to board the flight. White House Deputy National Security Adviser Tony Blinken said the U.S. was looking into the stolen passports, but that investigators had reached no conclusions. 
 
 Interpol has long sounded the alarm that growing international travel has underpinned a new market for identity theft: Bogus passports are mostly used by illegal immigrants, but also pretty much anyone looking to travel unnoticed such as drug runners or terrorists. More than 1 billion times last year, travelers boarded planes without their passports being checked against Interpol's database of 40 million stolen or lost travel documents, the police agency said. 
 
 Finding traces of an aircraft that disappears over sea can take days or longer, even with a sustained search effort. Depending on the circumstances of the crash, wreckage can be scattered over a large area. If the plane enters the water before breaking up, there can be relatively little debris. 
 
 __ 
 
 Associated Press writers Chris Brummitt in Hanoi, Rod McGuirk in Canberra, Australia, Didi Tang, Gillian Wong and Louise Watt in Beijing, Joan Lowy in Washington and Scott Mayerowitz in New York contributed this report. ||||| Teams from nine countries working non-stop, officials say, as hunt goes on for plane missing with 239 people on board 
 
 Search crews involving nine countries are working “every hour, every minute, every second” across a huge swathe of the South China Sea but have yet to find any evidence of the missing Malaysia Airlines flight, the country’s civil aviation chief said on Monday. 
 
 Almost 60 hours after flight MH370 vanished from radar screens in the early hours of Saturday officials remain “puzzled” by its sudden disappearance and are considering all possible angles, Azharuddin Abdul Rahman said. 
 
 “Unfortunately, we have not found anything that appears to be an object from the aircraft, let alone the aircraft,” he said. 
 
 The Beijing-bound flight was carrying 227 passengers and 12 crew when it went missing around 40 minutes after its 12.41am take-off from Kuala Lumpur, over the seas between Malaysia and Vietnam. The Boeing-777 was cruising at 35,000 feet when it disappeared in apparently good weather, gave no indication of any problems and did not issue a distress call. 
 
 Rahman added: “There are many theories that have been said in the media; many experts around the world have contributed their expertise and knowledge about what could happen, what happened....We are puzzled as well. 
 
 “To confirm what happened on that particular day on this ill-fated aircraft...we need concrete evidence, parts of the aircraft for us to analyse, for us to do forensic study.” 
 
 He said that the government had not discounted speculation about a hijack, but was looking at every possible explanation, noting that it took two years to determine the cause of the 2009 Air France crash. 
 
 He confirmed that five passengers had checked in for the flight but not boarded, adding that their baggage was removed from the aircraft as necessary in such cases. 
 
 Concerns that terrorist might be responsible have been fuelled by the fact two passengers were travelling on stolen European passports - although experts have said that fraudulent documents are reasonably common on regional flights for a variety of reasons. 
 
 The men who used them were of Asian appearance, Malaysia’s home minister had said late on Sunday. But Rahman said on Monday that they were of “non-Asian” appearance. 
 
 Asked by a reporter what they looked like “roughly,” he said: “Do you know of a footballer by the name of (Mario) Balotelli? He is an Italian. Do you know how he looks like?” 
 
 
 
 A reporter then asked, “Is he black?” and the aviation chief replied, “Yes.” 
 
 The passports were stolen from Luigi Maraldi and Christian Kozel in the last two years, and were listed as stolen on Interpol’s database. The international police agency said the documents had not been checked with its system and that it had long urged all countries to check passports systematically. 
 
 The suggestion that the plane may have turned back just before disappearing from radar screens - mooted by officials yesterday – remains unconfirmed, Rahman added. 
 
 Nine countries are now taking part in the search, which Rahman said covered the area within a 50 nautical mile radius of the aircraft’s last known position and the northern Straits of Malacca in case the plane had turned back. 
 
 “We are every hour, every minute, every second looking at every inch of the sea,” he said. 
 
 Forty ships are working round the clock, while 34 aircraft are working during daylight hours. Potential sightings of aircraft debris by Vietnamese searchers have not been verified, Rahman said. 
 
 There have been a few glimmers of hope, but so far no trace of the plane has been found. 
 
 On Sunday afternoon, a Vietnamese plane spotted a rectangular object that was thought to be one of the missing plane’s doors, but ships working through the night could not locate it. 
 
 Malaysian maritime officials found some oil slicks in the South China Sea and sent a sample to a lab to see if it came from the plane. Tests showed that the oil was not from an aircraft, Rahman said. 
 
 Malaysia Airlines said in a statement it posted today that its primary focus was caring for the families of passengers, some of whom it has already flown to Kuala Lumpur. It has also sent counsellors to Beijing as two-thirds of the travellers were Chinese. 
 
 “We appreciate the help we are receiving from all parties and agencies during this critical and difficult time...Malaysia Airlines is similarly anxious and we appreciate the patience, support and prayers from everyone,” it said. 
 
 But many of the Chinese passengers’ relatives have complained that the airline has so far given them little information or support and have chosen to stay in Beijing. 
 
 An editorial in the state-run Global Times newspaper attacked the airline and authorities on Monday, warning: “The Malaysian side cannot shirk its responsibilities. The initial response from Malaysia was not swift enough.” 
 
 It added: “There are loopholes in the work of Malaysia Airlines and security authorities. If it is due to a deadly mechanical breakdown or pilot error, then Malaysia Airlines should take the blame. If this is a terrorist attack, then the security check at the Kuala Lumpur airport and on the flight is questionable.” ||||| Story highlights China calls for Malaysia to pick up the pace in its search, state media reports 
 
 A U.S. intelligence official says stolen passports could be tied to human smuggling 
 
 Brother of missing passenger: We're holding out hope, because ... there are no answers" 
 
 Underwater search expert: "Crucial time is passing" 
 
 What made Malaysia Airlines Flight 370 go off the grid? Where is it now? And could two stolen passports be the key to unraveling what happened? 
 
 Questions such as these were more common than answers Monday as searchers kept looking for the Boeing 777 that vanished without a trace three days ago. 
 
 As boats and planes scoured the water, chasing a series of leads that proved false, authorities revealed new details in their investigation and speculation surged. Among the latest developments: 
 
 -- Two men who apparently boarded the plane with stolen passports -- and the man who bought their tickets -- have become one focus for investigators. So far, authorities haven't said who the men were or why they were on the flight. The FBI was running their thumbprints through a database on Monday after receiving them from Malaysian officials. One U.S. intelligence official noted that the circumstances surrounding the use of the stolen passports follows a pattern similar to human smuggling rings and might not have anything to do with the plane's disappearance. 
 
 -- The area that nearly three dozen aircraft and 40 ships from 10 countries are combing has grown. "Now it's a search area hundreds of miles big," Cmdr. William Marks of the U.S. Navy 7th Fleet told CNN. 
 
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 Flight 370: Areas being searched 
 
 -- It's too soon to know why the plane went missing, but investigators are weighing a number of possibilities and haven't ruled anything out. The possibility of terrorism is still on the table, though the U.S. intelligence official said that's looking less likely. 
 
 -- Family members of passengers are being told to prepare for the worst. But the brothers of Philip Wood, an American passenger who was on the plane, told CNN they're relying on faith to keep them going. "We're holding out hope," Tom Wood said, "because as of yet, there are no answers in any of this." 
 
 The mysteries surrounding Malaysia Airlines Flight 370 -- and the true identities of some of its passengers -- remain unsolved. 
 
 No emergency signal has been detected by any search vessel or aircraft. 
 
 "For the aircraft to go missing just like that ... as far as we are concerned, we are equally puzzled as well," said Azharuddin Abdul Rahman, director general of the Malaysian Civil Aviation Department. "We have to find the aircraft." 
 
 The stolen passports 
 
 It is perplexing enough that a jetliner seems to have vanished without a trace. Adding to the mystery is the news that at least two people on board were traveling on passports stolen from an Austrian and an Italian. 
 
 The FBI is running those passengers' thumbprints through its database, a law enforcement official told CNN. The thumbprints were taken at the airport check-in in Kuala Lumpur and were shared with intelligence and law enforcement agencies around the world by the Malaysian government. 
 
 Later Monday, a law enforcement official told CNN that information has been shared with various agencies that includes what may be the names of the two men who used stolen passports, and that so far nothing has come up to cause concerns. 
 
 Malaysian officials have also shared images of the men with the U.S. government, a U.S. intelligence official said. 
 
 "They will compare that to what we have in our terrorist databases. These are lists of people on no-fly lists, people with possible terrorist connections, people we have reasons to be suspicious of," U.S. Rep. Peter King told CNN's "The Lead." "We have these listings, and those names and those biometrics will be compared to those." 
 
 According to Thai police officials, an Iranian man by the name of Kazem Ali bought one-way tickets for the two men, describing them as friends who wanted to return home to Europe. While Ali made the initial booking by telephone, either Ali or someone acting on his behalf paid for the tickets in cash, according to police. 
 
 But CNN law enforcement analyst Tom Fuentes cautioned against concluding too much from details police apparently learned from a travel agency. 
 
 "We don't know if that information is trustworthy. We know that it's a lead and has been provided to the Royal Thai Police. They've furnished it back to the other agencies," said Fuentes, a former FBI assistant director. "But as far as I'm concerned, it still needs to be confirmed who this gentleman was." 
 
 Authorities have reviewed security footage from the airport and said the men who traveled on the stolen passports "are not Asian-looking men," Rahman said Monday. 
 
 A majority of the 239 people on the plane were from Asia, according to the airline's manifest. There were 154 people from China or Taiwan and 38 people from Malaysia aboard. 
 
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 The Italian whose name was on the plane's manifest, Luigi Maraldi, told reporters in Thailand over the weekend that he'd reported his passport stolen in August. 
 
 Interpol tweeted Sunday it was examining additional "suspect #passports." 
 
 "Whilst it is too soon to speculate about any connection between these stolen passports and the missing plane, it is clearly of great concern that any passenger was able to board an international flight using a stolen passport listed in INTERPOL's databases," said Interpol Secretary General Ronald K. Noble in a statement. 
 
 The passports were reportedly stolen in Thailand, and Thai Prime Minister Yingluck Shinawatra told CNN's "Amanpour" on Monday that police are investigating. 
 
 "Initially we don't know about their nationality yet," she said. "But we gave orders for the police to investigate the passport users. Because this is very important to Thailand, to give full cooperation to Interpol in the investigation about the passport users. We are now following this." 
 
 So far, nothing 
 
 Malaysia Airlines Flight 370 took off from Kuala Lumpur shortly before 1 a.m. Saturday (12 p.m. Friday ET). 
 
 The plane disappeared somewhere between Malaysia and Vietnam. Since then, teams of searchers from Vietnam, China, Singapore, Indonesia, the United States, Thailand, Australia, the Philippines and New Zealand have been working alongside Malaysians to scour the Gulf of Thailand, part of the South China Sea that lies between several Southeast Asian countries. 
 
 The focus has now shifted to the Andaman Sea, near Thailand's border, after radar data indicated the plane may have turned around to head back to Kuala Lumpur. 
 
 But the pilot apparently gave no signal to authorities that he was turning around. 
 
 Investigators have said several leads have turned out to be dead ends. 
 
 An oil slick that searchers had thought might be from the plane turned out to be fuel oil typically used in cargo ships, according to Rahman. 
 
 Other leads -- reports that a plane door and its tail had been spotted -- also turned out to be untrue. 
 
 China called on Malaysia to pick up the pace in its search, the state-run Xinhua news agency reported. 
 
 "We hope Malaysia can fully understand China, especially the mood of the Chinese passengers' families and speed up investigation, search and rescue efforts," Foreign Ministry spokesman Qin Gang told reporters, according to Xinhua. 
 
 Search and rescue officials said Monday they were expanding the search area to encompasses a larger portion of the Gulf of Thailand between Malaysia and Vietnam. 
 
 Authorities are sending ships to investigate a report of debris found south of Hong Kong, but it will likely be Tuesday before authorities know if there is anything to those reports, Rahman said. 
 
 From 7 a.m. to 7 p.m., planes flew over the vast waters. Ships searched through the night. 
 
 "Every day that goes by, it makes the search area much, much larger," said David Gallo, who helped lead the search for the wreckage of Air France Flight 447 after that plane crashed in 2009. 
 
 Looking for wreckage and flight data recorders in the water is no easy task, he told CNN's "The Situation Room." 
 
 "We've only explored about 7% of the world beneath the sea, and there's a reason for that. It's slow going, and it's difficult. So, with every day that passes by, crucial time is passing." 
 
 Terrorism concern 
 
 The passport mystery raised concerns about the possibility of terrorism, but officials cautioned that it was still too early to arrive at any conclusions. 
 
 One possible explanation for the use of the stolen passports is illegal immigration. 
 
 There are previous cases of illegal immigrants using fake passports to try to enter Western countries. And Southeast Asia is known to be a booming market for stolen passports. 
 
 Five passengers ended up not boarding the aircraft. Their bags were removed and were not onboard the jet when it disappeared, Rahman said at Monday's briefing. 
 
 Could the plane have been hijacked? "We are looking at every angle, every aspect," Rahman said. 
 
 "We are looking at every inch of the sea." 
 
 There has been some speculation that the flight might have been a test run for a terrorist organization planning a later attack. 
 
 The incident has some similarities to such incidents in the past, such as the 1994 bombing of a Philippine jetliner that investigators later learned was a test run for a wider plot to bomb numerous airliners, former U.S. Department of Transportation Inspector General Mary Schiavo told CNN on Monday. 
 
 But John Magaw, a former Transportation Security Administration official and U.S. Secret Service director, said his best guess is the Malaysia Airlines flight was not a test. 
 
 "They've already done the dry run," he said. "This was the actual flight." 
 
 Analysts warned that it's far too soon to know why the plane went missing or what caused it. 
 
 "We have speculation run amok, because we have no facts," said Michael Goldfarb, a former chief of staff for the Federal Aviation Administration. "Speculation on the cause is always wrong, because it's a unique accident. It rarely happens. 
 
 "And I do believe that they will find the so-called black boxes. ... They'll find where the plane is." 
 
 Agonizing wait 
 
 For the relatives of the 227 passengers and 12 crew members, the wait has been agonizing. 
 
 "As of yet, we know as much as everyone else," Tom Wood told CNN's "AC360" Monday. "It seems to be getting more bizarre, the twists in the story, where they can't find anything. So we're just relying on faith." 
 
 In Beijing, family members gathered in a conference room at a hotel complex. 
 
 More than 100 people signed a hand-written petition that demanded "truth" from the airline. They also urged the Chinese government to help them deal with Malaysian authorities. 
 
 Malaysia Airlines, which was helping family members apply for expedited passports, said it will fly out five relatives of each passenger to Kuala Lumpur. 
 
 A fuller picture of what happened may not become available until searchers find the plane and its flight data recorder. 
 
 And so far, that hasn't happened. ||||| Media playback is unsupported on your device Media caption Police chief Khalid Abu Bakar: "He [Iranian man] is not likely to be member of terrorist group" 
 
 Two men travelling on stolen passports on board a missing Malaysian airliner were Iranians with no apparent links to terrorist groups, officials say. 
 
 Malaysian police named one as Pouria Nour Mohammad Mehrdad, 18, and said he was probably migrating to Germany. 
 
 Interpol identified the other as Delavar Seyed Mohammadreza, 29. 
 
 Malaysia Airlines Flight MH370 from Kuala Lumpur to Beijing went missing on Saturday, after taking off with 239 on board. The search has been widened. 
 
 Image caption Pouria Nour Mohammad Mehrdad is second from the left. Delavar Seyed Mohammadreza, on the far right, travelled with him on the missing plane. 
 
 Image copyright Malaysian police Image caption Police released pictures of the two as they boarded the plane 
 
 Experts have said the presence of two people with stolen passports on a plane was a breach of security, but one that is relatively common in a region regarded as a hub for illegal migration. 
 
 Malaysia's police chief, Inspector General Khalid Abu Bakar, said the younger Iranian was "not likely to be a member of a terrorist group", adding that the authorities were in contact with his mother in Germany, who had been expecting her son to arrive in Frankfurt. 
 
 Speaking in Paris later on Tuesday, Interpol Secretary General Ronald Noble said the two men had travelled from Qatar's capital Doha on their Iranian passports, and switched to stolen Italian and Austrian passports to board the Malaysia Airlines flight. 
 
 Media playback is unsupported on your device Media caption The secretary general of Interpol Ronald Noble: "These two individuals were probably not terrorists" 
 
 "The more information we get, the more we are inclined to conclude it is not a terrorist incident," he added. 
 
 Without a trace 
 
 The authorities' statement supports an account given to the BBC by a young Iranian in Kuala Lumpur, who says he was a school friend of one of the men who boarded the airliner using stolen documents. 
 
 He says the friend and another Iranian stayed with him before taking the Malaysia Airlines flight, and that they had hoped to settle in Europe. 
 
 Reports from Thailand suggest that the tickets of the two men, routing them to Amsterdam via Beijing, had been bought through a Thai travel agent and an Iranian middleman. 
 
 Officials say they still have no idea what went wrong with the aircraft. 
 
 None of the debris and oil slicks spotted in the water so far have proved to be linked to the disappearance. 
 
 Media playback is unsupported on your device Media caption The BBC's Alice Budisatrijo says searchers are 'using the naked eye' to try to find the missing plane 
 
 Four areas of investigation were focused on the possibility of human agency, the police chief said: hijacking, sabotage, psychological problems or personal problems with passengers or crew. 
 
 Two-thirds of the passengers were Chinese. Others were from various Asian countries, North America or Europe. 
 
 Relatives have expressed frustration at the lack of information about the plane's fate. 
 
 At least 40 ships and 34 aircraft are taking part in the search in the seas off Vietnam and Malaysia. 
 
 Media playback is unsupported on your device Media caption The BBC's Richard Westcott examines how a plane can vanish without trace 
 
 Search teams from Australia, China, Thailand, Indonesia, Singapore, Vietnam, Philippines, New Zealand and the United States of America are assisting. 
 
 Civil aviation chief Azharuddin Abdul Rahman said on Tuesday that the search was being conducted "on both sides" of the Malay Peninsula. 
 
 The area has been expanded from 50 nautical miles (57 miles; 93km) from where the plane had disappeared - over waters between Malaysia and Vietnam - to 100 nautical miles. 
 
 Malaysia Airlines said it was considering the possibility that the aircraft had tried to turn back to an airport at Subang, near Kuala Lumpur, leaving its flight path. ||||| Investigators searching for a missing Malaysia Airlines plane that disappeared with 239 people on board have said all security checks were followed. 
 
 Malaysia's civil aviation chief said two passengers travelling on stolen passports - one issued by Italy and the other by Austria - were "not Asian-looking men". 
 
 Asked for a description of the pair, Azharuddin Abdul Rahman added: "Do you know a footballer by the name of (Mario) Balotelli? (This is) what he looks like. I don't want to dwell on this but the men are not Asian-looking." 
 
 Search teams are scouring vast areas of ocean for the missing flight 
 
 Mr Rahman also revealed the search area has been extended and said rescuers are responding to reports of debris floating in the sea near Hong Kong. 
 
 Meanwhile, samples of oil taken from a slick in the South China Sea came from a ship, not the missing aircraft, it has been confirmed. 
 
 It comes after a reported sighting of a life raft by the crew of a Vietnamese jet turned out to be a false alert. 
 
 Spotter planes and ships are involved in the search for the missing flight 
 
 Authorities admit they are "puzzled" by the "unprecedented" disappearance of flight MH370 mid-way between Kuala Lumpur and Beijing. 
 
 Security services are investigating whether the Boeing 777-200 was hijacked or destroyed in a terror attack. 
 
 Earlier reports of debris spotted in the South China Sea, including an aircraft door, have not been confirmed, while a possible sighting of a section of the plane's tail has been ruled out. 
 
 Investigators say Vietnam has not confirmed a possible plane door sighting 
 
 Sky's Jonathan Samuels, in Beijing, said authorities have warned against giving "false hope" to relatives by reporting every sighting of debris. 
 
 "They say it's very distressing and very upsetting for families to hear there may be something like a life raft out in the ocean, only to have their hopes dashed just a short time later," he said. 
 
 The two men travelling on stolen passports bought their tickets together and were due to fly to Europe after landing in Beijing. 
 
 The plane was flying between Kuala Lumpur and Beijing when it vanished 
 
 Search teams are scouring two vast areas of the ocean south-west of Vietnam 
 
 Malaysian police chief Khalid Abu Bakar said one of the mystery passengers had been identified as a non-resident of the country. 
 
 Officials are discussing whether images of the men should be made public as part of an appeal for information, while Interpol said additional "suspect" documents are under review. 
 
 Initial investigations suggest the plane disintegrated at about 35,000ft, according to the Reuters news agency. 
 
 Samples of oil taken from a slick did not come from the missing plane 
 
 Had the plane plunged into the sea and broken up on impact, search teams would have expected to find a concentrated pattern of debris, a source involved in the probe said. 
 
 The search, which involves teams from 10 countries, was widened after radar suggested the aircraft may have turned back before it vanished. 
 
 Rescuers have been concentrating their efforts on a 10,500 sq mile area of ocean that includes parts of the Gulf of Thailand and the South China Sea. 
 
 Investigators have told relatives to 'prepare for the worst' 
 
 Meanwhile, relatives of those on the flight are enduring an agonising wait for information and anger is growing in China about the lack of progress with the investigation. 
 
 Nearly two-thirds of the passengers were Chinese and if the loss of the plane is confirmed, it would be the country's second-worst air disaster. 
 
 In a scathing editorial, the Global Times newspaper, which has links to the Chinese Communist Party, said: "The Malaysian side cannot shirk its responsibilities. The initial response from Malaysia was not swift enough. 
 
 "There are loopholes in the work of Malaysia Airlines and security authorities." 
 
 :: Watch Sky News live on television, on Sky channel 501, Virgin Media channel 602, Freeview channel 82 and Freesat channel 202. ||||| KUALA LUMPUR, Malaysia (AP) — Military radar indicates that the missing Boeing 777 jet may have turned back before vanishing, Malaysia's air force chief said Sunday as authorities were investigating up to four passengers with suspicious identifications. 
 
 A Chinese relative of the passengers aboard the missing Malaysia Airlines plane passes a demand letter for the airlines, signed by other relatives, to the media at a hotel, in Beijing, China Sunday, March... (Associated Press) 
 
 Family members of passengers aboard a missing plane cry at a hotel in Putrajaya, Malaysia, Sunday, March 9, 2014. Military radar indicates that the missing Boeing 777 jet of Malaysia Airlines may have... (Associated Press) 
 
 Hugh Dunleavy, left, from commercial director of the Malaysia Airlines is escorted by an unidentified Chinese man after speaking for relatives or friends of passengers aboard the missing plane, in Beijing... (Associated Press) 
 
 This photo provided by Laurent Errera taken Dec. 26, 2011, shows the Malaysia Airlines Boeing 777-200ER that disappeared from air traffic control screens Saturday, taking off from Roissy-Charles de Gaulle... (Associated Press) 
 
 In this photo released by Malaysian Maritime Enforcement Agency, a patrol vessel of Malaysian Maritime Enforcement Agency searches for the missing Malaysia Airlines plane off Tok Bali Beach in Kelantan,... (Associated Press) 
 
 A Chinese relative of passengers aboard a missing Malaysia Airlines plane cries as she leaves a hotel room for relatives or friends of passengers aboard the missing airplane, in Beijing, China Sunday,... (Associated Press) 
 
 A vendor prepares newspapers carrying a headline story and pictures of Saturday's missing Malaysian Airlines plane, in Shah Alam, outside Kuala Lumpur, Malaysia, Sunday, March 9, 2014. An international... (Associated Press) 
 
 This screengrab from flightradar24.com shows the last reported position of Malaysian Airlines flight MH370, Friday night March 7, 2014. The Boeing 777-200 carrying 239 people lost contact over the South... (Associated Press) 
 
 Buddhist monks offer a special prayer for passengers aboard a missing plane, at Kuala Lumpur International Airport in Sepang, Malaysia, Sunday, March 9, 2014. Military radar indicates that the missing... (Associated Press) 
 
 A Chinese relative of passengers aboard a missing Malaysia Airlines plane, center, cries as she is escorted by a woman while leaving a hotel room for relatives or friends of passengers aboard the missing... (Associated Press) 
 
 The revelations add to the uncertainties surrounding the final minutes of flight MH370, which was carrying 239 people when it lost contact with ground controllers somewhere between Malaysia and Vietnam after leaving Kuala Lumpur early Saturday morning for Beijing. 
 
 A massive international sea search has so far turned up no trace of the plane, which lost contact with the ground when the weather was fine, the plane was already cruising and the pilots didn't send a distress signal — unusual circumstance for a modern jetliner operated by a professional airline to crash. 
 
 Vietnamese air force jets spotted two large oil slicks Saturday, but it was unclear if they were linked to the missing plane, and no debris was found nearby. 
 
 Air force chief Rodzali Daud didn't say which direction the plane veered when it apparently went off course, or how long it flew in that direction. 
 
 "We are trying to make sense of this," he told a media conference. "The military radar indicated that the aircraft may have made a turn back and in some parts, this was corroborated by civilian radar." 
 
 Malaysia Airlines Chief Executive Ahmad Jauhari Yahya said pilots were supposed to inform the airline and traffic control authorities if the plane does a U-turn. "From what we have, there was no such distress signal or distress call per se, so we are equally puzzled," he said. 
 
 Authorities were checking on the suspect identities of at least two passengers who appear to have boarded with stolen passports. On Saturday, the foreign ministries in Italy and Austria said the names of two citizens listed on the flight's manifest matched the names on two passports reported stolen in Thailand. 
 
 Malaysian Transport Minister Hishammuddin Hussein said that authorities were looking at two more possible cases of suspicious identities. He said Malaysian intelligence agencies were in contact with their international counterparts, including the FBI. He gave no more details. 
 
 "All the four names are with me and have been given to our intelligence agencies," he said. "We are looking at all possibilities." 
 
 The stolen passports, and the sudden disappearance of the plane that experts say is consistent with a possible onboard explosion, strengthened existing concerns about terrorism as a possible cause for the disappearance. Al-Qaida militants have used similar tactics to try and disguise their identities. 
 
 Despite that, other possible causes would seem just as likely at this stage, including a catastrophic failure of the engines or the plane itself, extreme turbulence and pilot error or even suicide. Establishing a cause with any certainty will need data from flight recorders and a detailed examination of any debris, something that will take months if not years. 
 
 European authorities on Saturday confirmed the names and nationalities of the two stolen passports: One was an Italian-issued document bearing the name Luigi Maraldi, the other Austrian under the name Christian Kozel. 
 
 A telephone operator on a China-based KLM hotline on Sunday confirmed "Maraldi" and "Kozel" were both booked to leave Beijing on a KLM flight to Amsterdam on March 8. Maraldi was then to fly to Copenhagen on KLM on March 8, and Kozel to Frankfurt on March 8. 
 
 She said the pair booked the tickets through China Southern Airlines so she had no information on where they bought them. 
 
 Having an onward reservation from Beijing would have meant the pair, as holders of EU passports, would not have needed a visa for China. Beyond that, it was unclear whether this had any possible implications for the investigation. 
 
 A total of 22 aircraft and 40 ships have been deployed to the area by Malaysia, Thailand, Singapore, Indonesia, China and the United States, not counting Vietnam's fleet. 
 
 Two-thirds of the jet's passengers were Chinese. The rest were from elsewhere in Asia, North America and Europe. 
 
 After more than 30 hours without contact with the aircraft, Malaysia Airlines told family members they should "prepare themselves for the worst," Hugh Dunleavy, the commercial director for the airline told reporters. 
 
 Finding traces of an aircraft that disappears over sea can take days or longer, even with a sustained search effort. Depending on the circumstances of the crash, wreckage can be scattered over many square kilometers (miles). If the plane enters the water before breaking up, there can be relatively little debris. 
 
 A team of American experts was en route to Asia to be ready to assist in the investigation into the crash. The team includes accident investigators from National Transportation Safety Board, as well as technical experts from the Federal Aviation Administration and Boeing, the safety board said in a statement. 
 
 Malaysia Airlines has a good safety record, as does the 777, which had not had a fatal crash in its 19-year history until an Asiana Airlines plane crashed last July in San Francisco, killing three passengers, all Chinese teenagers. 
 
 Jason Middleton, the head of the Sydney-based University of New South Wales' School of Aviation, said terrorism or some other form of foul play seemed a likely explanation. 
 
 "You're looking at some highly unexpected thing, and the only ones people can think of are basically foul play, being either a bomb or some immediate incapacitating of the pilots by someone doing the wrong thing and that might lead to an airplane going straight into the ocean," Middleton said. "With two stolen passports (on board), you'd have to suspect that that's one of the likely options." 
 
 But Clive Williams, a counter-terrorism expert at Australia's Macquarie University and a former military intelligence officer, said he doubted the two stolen passports aboard the flight were related to the disaster. The latest Interpol data showed there were 39 million lost or stolen passports reported as of Dec. 2013. 
 
 "Any flight of that size in Asia would be carrying a couple of people with false passports," he said. "When you think about the number of passports that have been stolen or gone missing around the world ... it could be related, but it's probably not." 
 
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 Brummitt reported from Hanoi, Vietnam. 
 
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 Associated Press journalist Rod McGuirk in Canberra; Didi Tang, Gillian Wong and Louise Watt in Beijing; Joan Lowy in Washington; and Scott Mayerowitz in New York contributed this report.
– The fate of the missing Malaysia Airlines flight and the 239 onboard continues to stump officials. Authorities are considering every possible explanation for the disappearance, says Malaysia's civil aviation boss, Azharuddin Abdul Rahman. Among those explanations are engine failure, pilot error, or possibly suicide. But so far, searches have yielded little information—even with 40 ships and 34 aircraft investigating a radius of 50 nautical miles around where the plane dropped off radar screens, the AP reports. Nine countries are involved in the search, and they're working "every hour, every minute, every second," Rahman adds, per the Guardian. It's now after dark in the area, and the search will resume tomorrow. In other search news: As for hijacking, "we are not discounting this," says Rahman, via the AP. Malaysia says it has CCTV visuals of two people traveling with stolen passports. Officials said today at a news conference that the two were not "Asian-looking people," as per the BBC. One-way tickets under the names on the stolen passports—Luigi Maraldi and Christian Kozel—were issued at a Thai travel agency. Passengers traveling under those names were also booked on a one-way flight from Beijing to Amsterdam Saturday, says a rep for Royal Dutch Airlines. Maraldi was then due to fly to Copenhagen, while Kozel was set to go to Frankfurt, Germany. Malaysia is now downplaying reports suggesting Vietnam had discovered possible debris. "We have not found anything that appear to be objects from the aircraft, let alone the aircraft," says Rahman, per CNN. Officials had believed they'd spotted a life raft in the water, and helicopters were rushed to the spot—only to find a "moss-covered cap of a cable reel," NBC News reports. Meanwhile, oil slicks discovered in the South China Sea are not connected to the aircraft, Sky News confirms via AFP.