A Malaysia Airlines jet was shot down by a surface-to-air missile Thursday over separatist-controlled eastern Ukraine, apparently killing all 298 people on board and dramatically raising stakes in the conflict with the Kremlin-backed forces. 
 
 U.S. intelligence sources said tracking data from spy satellites and radar confirmed that the Boeing 777 en route from Amsterdam to Kuala Lumpur was hit in midair, but they couldn't immediately determine where the missile was launched. 
 
 Ukrainian officials said that Russia had recently supplied the separatists with the mobile Buk surface-to-air launching system, and that the military had not fired any antiaircraft missiles during the conflict with the separatists, which began in mid-April. A number of Ukrainian military aircraft have been shot down by the separatists. 
 
 Although Russia denied involvement, the downing of a passenger jet flying on a heavily traveled international route could sharply increase pressure on Russian President Vladimir Putin, who is accused by the United States, its allies and the Ukrainian government of backing the separatists. 
 
 Before the loss of the passenger jet Thursday, fighting in eastern Ukraine had claimed at least 500 lives in the four months since Russia seized and annexed Ukraine's Crimean peninsula, inspiring the separatists now occupying much of Ukraine's Donetsk and Luhansk regions. 
 
 On Wednesday, the Obama administration stepped up sanctions against Russia for supporting the separatists, targeting some of the country's largest financial institutions, energy companies and weapons firms. 
 
 The loss of another plane dealt a new blow to Malaysia Airlines. It hasn't solved the mystery of what happened to Flight 370, which disappeared on its way from Kuala Lumpur to Beijing in March. 
 
 Ukrainian Security Service communications intercepts made public after the early evening crash of Flight 17 suggest coordination between the separatists and Russian fighters across the border. 
 
 Malaysia Airlines said it lost contact with Flight 17, carrying 283 passengers and 15 crew members, after the aircraft failed to confirm its entry into Russian airspace on schedule at 5:20 p.m. The last contact was recorded about 4:20 p.m. by air traffic controllers. 
 
 The plane “disappeared from radar at [33,000 feet] and then crashed near the city of Shakhtersk in Ukraine's Donetsk region,” the Interfax-Ukraine news agency reported. 
 
 Witnesses in the militant-held crash area about 25 miles west of the Russian border described a gut-wrenching scene. 
 
 “Distorted bodies of dead people and body parts are lying around everywhere in an open field,” Sergei Kavtaradze, a member of the Security Council of the separatists' self-proclaimed Donetsk People's Republic, said in a phone interview. 
 
 Two things were clear from rescue workers' reports, he said: Everyone on board was killed, and it “was not us who shot down the plane because we don't have this hardware.” 
 
 Ukrainian officials disputed that assertion. Anton Gerashchenko, an advisor to the Interior Ministry, said Russia had recently supplied mobile missile systems to the separatists that are capable of taking down a plane at that altitude. 
 
 He demanded that Putin face an international tribunal in the disaster. 
 
 Neither the Kremlin nor major Russian media responded to the accusations that Moscow was behind the jet's downing. But Putin told his economic advisors meeting early Friday that the disaster was Ukraine's fault because of its offensive against separatists. 
 
 “This tragedy would not have happened if there were peace on this land, if the military actions had not been renewed in southeastern Ukraine. And, certainly, the state over whose territory this occurred bears responsibility for this awful tragedy,” the Kremlin news service quoted him as saying. 
 
 Ukrainian officials earlier Thursday accused Russian forces of being behind the downing the day before of a Ukrainian SU-25 ground-support warplane near Donetsk. 
 
 Shortly after the airliner went down, the former Russian special forces officer commanding the separatists in eastern Ukraine claimed responsibility for shooting down an AN-26 Ukrainian military transport plane. 
 
 “We warned them not to fly in our skies,” Igor Strelkov said on his Facebook page. “Peaceful people didn't suffer.” 
 
 He posted a video that later was removed from the page. 
 
 Pro-Russia separatists were the first to reach the crash site. 
 
 “Our self-defense units are already on the site,” said Andrei Purgin, first deputy premier of the breakaway region. “They already reported many dead passengers, including children.” 
 
 Sergei Taruta, the Kiev-appointed governor of the Donetsk region sidelined by the militants, said the separatists were blocking the crash site. 
 
 Russia's RIA Novosti news agency quoted Donetsk separatist leader Oleksandr Boroday as saying the separatists were calling a two- to three-day cease-fire to facilitate investigation of the crash. Boroday was quoted as saying the incident appeared to have been a “provocation.” 
 
 In spite of the conflict in eastern Ukraine, dozens of Europe-to-Asia flights have been passing over the region each day, aviation industry experts say. 
 
 Ukrainian officials had closed airspace below 32,000 feet, an altitude just below that at which the Malaysian jet was flying. 
 
 Mark Duell, vice president of operations at the flight tracking website FlightAware.com, said that flights from carriers that include Transaero Airlines, Emirates Airlines and Singapore Airlines have traveled over the region. 
 
 “We haven't found an airline that's been avoiding it previous to today,” he said. “Of course now that's changed.” 
 
 President Obama said the U.S. government was offering “any assistance we can to help determine what happened and why.” 
 
 Obama learned of the plane's downing while speaking on the phone with Putin on Thursday morning. Putin had requested the call with Obama to discuss the latest round of economic sanctions imposed by Washington and other Western governments. 
 
 News of the plane crash began to break while the two leaders spoke, White House Press Secretary Josh Earnest said later, and Putin mentioned the reports to Obama during the call. 
 
 Malaysian Prime Minister Najib Razak issued a statement lamenting the “terrible and deeply shocking news” of the second loss of a Malaysia Airlines 777 this year. 
 
 On March 8, Flight 370 bound for Beijing went missing, setting off a global search that has riveted international attention. No trace of the flight has been located despite the costliest lost-aircraft search in history. ||||| A man stands at the crash site July 26 of Malaysia Airlines Flight 17. (Photo: Bulent Kilic, AFP/Getty Images) 
 
 Data downloaded from a black box retrieved from the wreckage of Malaysia Airlines Flight 17 are consistent with a missile attack, national news media are reporting, citing an unidentified European air safety official. 
 
 The source told CBS News the findings indicate the plane's fuselage was hit by shrapnel from a missile explosion. 
 
 "It did what it was designed to do — bring down airplanes," the source told CBS. 
 
 A thorough investigation of the site, however, remains elusive 10 days after the jetliner crashed in an area of eastern Ukraine held by ethnic-Russian separatists. On Sunday, a team of international police officers cleared by separatist leader Alexander Borodai to visit the site canceled the trip when fighting broke out in the area. 
 
 Alexander Hug, the deputy head of a monitoring team from the Organization for Security and Cooperation in Europe, said it was too dangerous for the unarmed officers to travel to the site. 
 
 Hug said the police mission, which is comprised of officers from the Netherlands and Australia, will reconsider resuming operations if security improves. Australian prime minister Tony Abbott had said earlier Sunday that unarmed Australian police would be sent to the crash site as part of a Dutch-led police force to secure the area and help recover victims' remains. Crash victims include 37 Australians. 
 
 Ukraine's National Security Council said that government troops have encircled Horlivka, a key rebel stronghold near the crash site. A representative of the separatist military command in Donetsk confirmed that there had been fighting in Horlivka, but said that rebel fighters were holding their positions. 
 
 The Amsterdam-to-Kuala Lumpur flight crashed July 17, killing all 298 people on board, most of them Dutch citizens. U.S. and Ukrainian officials say it was shot down by a missile from rebel territory, most likely by mistake. 
 
 Ukrainian foreign minister Pavlo Klimkin, speaking Sunday on CBS' Face the Nation, that Russia was responsible for the air tragedy. He acknowledged that separatists could easily buy some weapons on the black market, but that there are limits. 
 
 "How can you buy on the black market a highly sophisticated, anti-aircraft missile capable to shoot down planes at the altitude of 10,000 meters?" Klimkin said. "You imagine that the terrorists can operate highly sophisticated weapons there? It's of course about responsibility of those (Russians) who bring also across the border all inflow of weapons and weaponry.'' 
 
 Russian Deputy Defense Minister Anatoly Antonov has repeatedly dismissed accusations that ethnic-Russian separatists — or Russians themselves — shot down the plane, saying that if the U.S. officials had proof "how come they have not been made public?" 
 
 On Saturday, the parents of a 25-year-old victim visited the site. Angela Rudhart-Dyczynski and Jerzy Dyczynski traveled from Perth, Australia, and had to cross dangerous pro-Russian rebel-held territory to honor their daughter, Fatima. 
 
 "We have promised our daughter we will come here," Rudhart-Dyczynski told NBC News. 
 
 Flights from Ukraine to the Netherlands have taken 227 caskets containing victims of the plane disaster. Officials say the exact number of people held in the caskets still needs to be determined by forensic experts in the Netherlands. 
 
 Ukraine's National Security Council spokesman Andrei Lysenko said that Ukrainian troops were engaging rebels in fighting at several locations Sunday, including near the town of Debaltseve, which is 15 miles northwest of the crash site. 
 
 The Malaysia Airlines disaster prompted some expectation in the West that Russia would scale back its involvement in the uprising in Ukraine's east. However, Russia launched artillery attacks from its soil into Ukraine on Friday, while the United States said it has seen powerful rocket systems moving closer to the Ukraine border. 
 
 Contributing: Natalie DiBlasio and Martha T. Moore, USA TODAY; Associated Press 
 
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– A Malaysia Airlines passenger plane crashed in Ukraine this morning, and all 283 passengers and 15 crew are feared dead, reports Reuters. A Ukrainian interior ministry official says the Boeing 777 was shot down by a surface-to-air missile, though it's too early to confirm the claim. (US intelligence agrees that a missile is to blame.) The plane, which originated in Amsterdam and was bound for Kuala Lumpur, was flying at 33,000 feet when it "began to drop; afterwards it was found burning on the ground on Ukrainian territory," a witness tells Interfax. It came down over territory held by separatists about 25 miles short of the Russian border, near the city of Donetsk, reports the LA Times. The region has seen fierce fighting in recent days. Immediately afterward, Ukraine President Petro Poroshenko said his troops "did not take action against any airborne targets," and pro-Russian separatists also denied responsibility. The plane appeared to have broken apart before hitting the ground, reports the AP, with one of its reporters counting at least 22 bodies at the crash site. President Obama and Russian President Vladimir Putin spoke by phone about the disaster, though no details about the discussion were immediately released. Malaysia Airlines, still reeling from the disappearance of another passenger jet, confirmed via Twitter that it "has lost contact of MH17 from Amsterdam. The last known position was over Ukrainian airspace." The airline's initial statement is here.