Media playback is unsupported on your device Media caption A child describes his mother "falling to the floor", as James Robbins reports 
 
 France's foreign minister has said a "reaction with force" could be needed if Syria is proved to have used chemical weapons against civilians. 
 
 Laurent Fabius's comments come a day after Syrian activists said hundreds of people died in such attacks in the Ghouta area of the capital, Damascus. 
 
 The UN has asked Syria to allow UN weapons inspectors already in the country to be allowed to investigate. 
 
 But there is no sign as yet that Damascus will allow this. 
 
 The UN team arrived in the city on Sunday and are staying about 15km (10 miles) from the site of the recent attacks. 
 
 Analysis The chances of the UN chemical weapons inspectors in Syria accessing the true site of Wednesday's alleged chemical attack in time to make a clear judgement on responsibility are slim. It took months to negotiate permission for them to visit other sites around the country. The Syrian government, backed by Russia, is resisting calls to give them access to the eastern Damascus suburb of Ghouta where this apparent atrocity took place. Part of the reason is the area is contested between government forces and rebels and is therefore unsafe. If an agent such as sarin has been used, the UN team would need to get to the site within days before traces become so faint as to be inconclusive. And if, as the opposition claims, it was a government attack, then a delay of days or weeks would give it enough time for forensic evidence to become controversial and for evidence of munitions used to be removed. The Syrian government insists it was the rebels who carried out the attack. 
 
 But they only have a mandate to visit three sites previously agreed between the UN and the Syrian government, including the northern town of Khan al-Assal, where some 26 people were killed in an alleged chemical attack in March. 
 
 The Syrian government has described the latest allegations as "illogical and fabricated". The Syrian army said opposition forces had made up the claims to divert attention from their recent huge losses. 
 
 Heavy shelling continued around Ghouta on Thursday, reports say. 
 
 'Red lines crossed' 
 
 A spokesman for Ban Ki-moon, Eduardo del Buey, said on Thursday that the secretary general Ban Ki-moon believed the attacks "need to be investigated without delay". 
 
 Mr Ban was sending his disarmament chief Angela Kane to Damascus to press for an investigation, he said. 
 
 Earlier, Mr Fabius told the French BFM TV channel that if the use of chemical weapons was confirmed, "France's position is that there must be a reaction, a reaction that could take the form of a reaction with force". 
 
 He did not elaborate on whether that meant backing military action, but did rule out the idea of deploying troops inside Syria. 
 
 The US state department said it had yet to "conclusively determine" what had taken place in Damascus, but that it was urgently gathering information. 
 
 Media playback is unsupported on your device Media caption US state department spokeswoman Jen Psaki: ''The president, of course, has a range of options'' 
 
 If President Bashar al-Assad's government was found to be behind a chemical weapons attack it would be "an outrageous and flagrant escalation", spokeswoman Jen Psaki said. 
 
 President Barack Obama warned last year that the use of such weapons would cross a "red line". 
 
 The British Foreign Office said earlier in a statement that the UK and 36 other countries had formally referred the latest allegations to Mr Ban, and called for inspectors "to be granted the necessary access to enable their investigation into these latest allegations as a matter of urgency". 
 
 "We believe a political solution is the best way to end the bloodshed," said the statement, but added that the UK has "said many times we cannot rule out any option... that might save innocent lives in Syria". 
 
 Turkish Foreign Minister Ahmet Davutoglu also stressed the need for an urgent response, and criticised the lack of UN action. 
 
 Image caption Video footage and photographs have been posted online appearing to show civilians, including children, suffering the effects of a chemical agent. In pictures: Damascus attacks How should the world respond? 
 
 On Wednesday, the UN Security Council failed to agree on a statement condemning the attack at an emergency meeting. 
 
 It was blocked by China and Russia, which have repeatedly backed the Syrian government since the crisis began. 
 
 Russia is supporting calls for an investigation, however, because it believes the opposition might have carried out the attack itself, as "premeditated provocation" in an attempt to win the backing of the UN. 
 
 Disturbing footage 
 
 Opposition activists said that more than 1,000 people were killed after government forces launched rockets with toxic agents into the Damascus suburbs in the Ghouta region early on Wednesday. 
 
 Chemical weapons claims Khan al-Assal, 19 March 2013 - Syrian state media accuse rebels of killing 31 people with rockets containing "chemical materials". Rebels blame the army for the attack. 
 
 - Syrian state media accuse rebels of killing 31 people with rockets containing "chemical materials". Rebels blame the army for the attack. Al-Otaybeh, 19 March 2013 - Opposition activists allege an attack in which six people are reported dead, apparently in reprisal for gains made by rebel forces. 
 
 - Opposition activists allege an attack in which six people are reported dead, apparently in reprisal for gains made by rebel forces. Adra, 24 March 2013 - The LCC activist network say two people are killed in an attack. 
 
 - The LCC activist network say two people are killed in an attack. Sheikh Maqsoud, Aleppo, 13 April 2013 - At least three people are killed in an attack; internet footage of the victims shows symptoms consistent with exposure to nerve gas. 
 
 - At least three people are killed in an attack; internet footage of the victims shows symptoms consistent with exposure to nerve gas. Saraqeb, 29 April 2013 - Eyewitnesses say canisters containing a poisonous gas are dropped from a helicopter above the town. Eight people are injured, one of whom later dies. 
 
 - Eyewitnesses say canisters containing a poisonous gas are dropped from a helicopter above the town. Eight people are injured, one of whom later dies. Ghouta, 21 August 2013 - By far the most serious alleged incident, with hundreds reported dead in attacks on the outskirts of Damascus Q&A: Damascus 'toxic attacks' Syria chemical weapons allegations Syria's chemical weapons stockpile How to investigate chemical arms allegations 
 
 The BBC has been unable to independently confirm the death toll. 
 
 Activists said Wednesday's attack took place as part of heavy government bombardment in the region surrounding Damascus, with government forces trying to drive out rebel forces. The areas affected included Irbin, Duma and Muadhamiya. 
 
 Video footage shows dozens of bodies with no visible signs of injuries, including small children, and survivors being treated in makeshift hospitals, with victims, including many children, having convulsions. 
 
 Chemical weapons experts have told the BBC that footage appears genuine and that the injuries shown are consistent with nerve agents. 
 
 While it is not clear how many died in the bombardment of the sites and how many deaths were due to any exposure to toxic substances, experts say it would be almost impossible to fake so many dead and injured including children and babies. 
 
 Both the rebels and government forces have accused each other of using chemical weapons throughout the 28-month conflict. 
 
 Syria is believed to have large undeclared stockpiles of mustard gas and sarin nerve agent. 
 
 The government has implied it has chemical weapons, but said they would not be used against civilians. 
 
 More than 100,000 people are believed to have been killed during the 28-months of conflict Syria. ||||| Image caption The convoy carrying UN chemical weapons inspectors to the sites was targeted by snipers 
 
 Diplomatic pressure on Syria has failed and the UK is considering its response to a suspected chemical attack, Foreign Secretary William Hague says. 
 
 He told the BBC it would be possible for the UK and its allies to respond without the UN's unanimous backing. 
 
 In Syria, UN inspectors visited the site of the suspected attack after their convoy was shot at by snipers. 
 
 The PM is cutting his holiday short and is expected to hold a National Security Council meeting on Wednesday. 
 
 Deputy Prime Minister Nick Clegg has also cancelled a visit to Afghanistan to meet British troops. 
 
 Downing Street said a decision on whether to recall Parliament would be made on Tuesday. 
 
 The suspected chemical attack took place on Wednesday near the Syrian capital Damascus, and reportedly killed more than 300 people. 
 
 Weapons inspectors carried out tests at the scene on Monday after unidentified snipers shot at one of their vehicles, a UN spokesman said. 
 
 Media playback is unsupported on your device Media caption William Hague: UN Security Council has not shouldered its responsibilities 
 
 Mr Hague told BBC Radio 4's Today programme while he could not go into options or a timetable for action, he was not "going to rule anything in or out". 
 
 "We, the United States, many other countries including France, are clear that we can't allow the idea in the 21st century that chemical weapons can be used with impunity," he said. 
 
 A Downing Street spokesman said Prime Minister David Cameron had called Russia's President Vladimir Putin on Monday afternoon to discuss Syria and that they had reiterated the position that the use of chemical weapons should merit a "serious response" from the international community. 
 
 But while Mr Cameron "made clear there was little doubt" the attack was carried out by the Syrian regime, Mr Putin "said they did not have evidence of whether a chemical weapons attack had taken place or who was responsible," the spokesman said. 
 
 MPs are due to return to the Commons on 2 September but there have been demands for Parliament to be recalled. 
 
 Analysis Whitehall officials say no firm decision is likely to be taken on how Britain will respond to last week's alleged chemical attack in Syria until at least Wednesday. That is when David Cameron will be chairing a session of the National Security Council, attended by military and intelligence chiefs and senior ministers. It follows intense consultations between London and Washington with Downing Street keen to stress the two countries are acting in concert. Any military response, if it's decided on, is most likely to be confined to a one-off or limited guided missile strikes on selected Syrian military targets using Tomahawk cruise missiles fired from US Navy warships stationed hundreds of miles away in the eastern Mediterranean. US vessels there are reported to have about 400 such missiles onboard, while a Royal Navy submarine in the region can also carry cruise missiles. But Russia, Syria and Iran have all issued strong warnings against any western military action. 
 
 Labour's shadow foreign secretary Douglas Alexander said he would "expect the prime minister to make his case to Parliament" before a decision was made about UK involvement. 
 
 The prime minister also had phone calls with other leaders, including US President Barack Obama, this weekend, where they agreed on the need to take "strong action". 
 
 He will return several days early from his holiday in Cornwall with his family so he can chair Wednesday's high-level security briefing of senior ministers and defence and intelligence chiefs. 
 
 It is understood the most likely military response would be a one-off or limited guided missile strikes on Syrian military targets fired from US Navy warships, says BBC security correspondent Frank Gardner. 
 
 Prof Michael Clarke, of the Royal United Services Institute, said: "Military advice to politicians in the US and the UK is 'don't think you can dabble in this - you have to go in with both feet'". 
 
 He told the BBC's PM programme limited air strikes might inconvenience the regime but were no guarantee you could stop it. 
 
 Other options - such as a no-fly zone or a safe haven - would have to be led by the US, and at the moment most of the "sabre-rattling" was coming from France and the UK - not the US, he added. 
 
 Whitehall officials have told the BBC the next key decisions would probably be taken at Wednesday's National Security Council meeting. 
 
 'Humanitarian need' 
 
 Mr Hague said diplomatic methods to resolve the civil war in Syria had "failed so far". 
 
 Media playback is unsupported on your device Media caption Russian Foreign Minister Sergei Lavrov: "They [the West] have not been able to come up with any proof but are saying at the same time that the red line has been crossed" 
 
 He said the UN Security Council, split over Syria, had not "shouldered its responsibilities". 
 
 The council is made up of 15 members including permanent members China, Russia, France, the US and the UK which have the power to veto any resolution. 
 
 But any action could be taken "without complete unity on the UN Security Council", he said. 
 
 He said a response could be "based on great humanitarian need and distress" and "in accordance with international law". 
 
 The foreign secretary said the suspected chemical attack was carried out by Syrian President Bashar al-Assad's regime but it blames rebel forces saying footage of the attack was "fabricated". ||||| Media playback is unsupported on your device Media caption The BBC's Yolande Knell: "The UN has always said the safety of its team is paramount" 
 
 Unidentified snipers have opened fire on a convoy of UN experts investigating suspected chemical weapons attacks in Syria's capital, the UN has said. 
 
 One car was shot at "multiple times", forcing the convoy to turn back. 
 
 Syrian state media blamed opposition "terrorists" for the attack, though the claim could not be verified. 
 
 The UN team later resumed its mission, entering the western district of Muadhamiya to gather evidence, before returning to central Damascus. 
 
 Hundreds died in alleged attacks on Wednesday in five districts near Damascus. 
 
 The US said there was little doubt that Syrian forces used chemical weapons in the attacks, which reportedly killed more than 300 people in rebel-held areas. 
 
 Syrian President Bashar al-Assad dismissed the accusation as "an insult to common sense" and warned the US against military intervention. 
 
 "If someone is dreaming of making Syria a puppet of the West, then this will not happen," he told the Russian newspaper Izvestiya. 
 
 'Intimidation' 
 
 The 20-member UN inspection team has been in Syria since 18 August to look into three earlier suspected chemical attacks. They were given permission on Sunday to examine the Damascus locations. 
 
 Image caption The UN inspectors have been talking to doctors in Muadhamiya 
 
 The experts intend to take soil, blood, urine and tissue samples for laboratory testing but they are unlikely to apportion blame for any of the attacks. 
 
 Video footage posted online appears to show UN inspectors in Muadhamiya taking samples and talking to residents. 
 
 They went to a Red Crescent centre and spoke to doctors, opposition activists said. 
 
 On the video, which the BBC has not been able to fully authenticate, one resident is heard telling an inspector of heavy raids on the district, with "over 600 canister strikes...12 tanks, 100 soldiers". 
 
 Shortly after setting out from their hotel in Damascus, the inspectors' cars came under fire "multiple times by unidentified snipers", according to a statement from the UN. 
 
 Analysis Whitehall officials say no firm decision is likely to be taken on how Britain will respond to last week's alleged chemical attack in Syria until at least Wednesday. That is when UK PM David Cameron will be chairing a session of the National Security Council, attended by military and intelligence chiefs and senior ministers. It follows intense consultations between London and Washington with Downing Street keen to stress the two countries are acting in concert. Any military response, if it is decided on, is most likely to be confined to a one-off or limited guided missile strikes on selected Syrian military targets using Tomahawk cruise missiles fired from US Navy warships stationed hundreds of miles away in the eastern Mediterranean. US vessels there are reported to have around 400 such missiles onboard, while a Royal Navy submarine in the region can also carry cruise missiles. But Russia, Syria and Iran have all issued strong warnings against any western military action. 
 
 The team returned safely back to the government checkpoint before setting out again. 
 
 The convoy was "deliberately targeted" and it seemed someone was trying to intimidate the team, the UN Secretary General's spokesman, Farhan Haq, told the BBC. 
 
 The inspectors have now returned to their hotel and are expected to resume their work on Tuesday. 
 
 Military action 
 
 A year ago, US President Barack Obama said the use of chemical weapons by the Syrian government would be "a red line" that could trigger US military action. 
 
 Washington has recently bolstered its naval presence in the eastern Mediterranean, and military leaders from the US, UK and their allies are meeting in Jordan. 
 
 But the UN Security Council remains divided, with China and Russia appearing unlikely to drop their objection to stricter sanctions on Mr Assad's government. 
 
 Chinese Foreign Minister Wang Yi said on Monday that diplomats should be cautious in dealing with the chemical weapons issue, and Moscow warned Western nations not to prejudge the outcome of the inspections. 
 
 Western politicians have begun to suggest taking action outside of the UN system. 
 
 UK Foreign Secretary William Hague told the BBC that action could be taken without UN approval if there was "great humanitarian need" in Syria. 
 
 His French counterpart Laurent Fabius suggested the UN Security Council could be bypassed "in certain circumstances". 
 
 Media playback is unsupported on your device Media caption William Hague: UN Security Council has not shouldered its responsibilities 
 
 But in his latest comments on the crisis, Russian Foreign Minister Sergei Lavrov said any intervention in Syria without a UN mandate would be a "grave violation of international law". 
 
 The West, he told a news conference in Moscow, had not been able to come up with any proof of chemical weapons use while "saying at the same time that the red line has been crossed and there can be no delay". 
 
 'Neurotoxic symptoms' 
 
 Western officials were unimpressed with Syria's decision to allow in the UN experts. 
 
 Mr Hague said evidence could have been tampered with, degraded or destroyed in the five days since the attack. 
 
 A senior White House official, quoted by AP news agency, dismissed the visit as "too late to be credible". 
 
 Medecins Sans Frontieres (MSF) said on Saturday that three hospitals it supports in the Damascus area had treated about 3,600 patients with "neurotoxic symptoms" on Wednesday morning, of whom 355 had died. 
 
 While MSF said it could not "scientifically confirm" the use of chemical weapons, staff at the hospitals described a large number of patients arriving in the space of less than three hours with symptoms including convulsions, pinpoint pupils and breathing problems. 
 
 Syria's security forces are widely believed to possess large undeclared stockpiles of mustard gas and sarin nerve agent. 
 
 It is one of seven countries that have not joined the 1997 convention banning chemical weapons. ||||| BEIRUT (Reuters) - U.N. weapons experts are due on Monday to inspect a site where poison gas killed many hundreds of people in Damascus suburbs, amid calls from Western capitals for military action to punish the world's worst apparent chemical weapons attack in 25 years. 
 
 Syria agreed on Sunday to allow the inspectors to visit the site. The United States and its allies say evidence has been destroyed by government shelling of the area over the past five days, and the Syrian offer to allow inspectors came too late. 
 
 Washington has faced calls for action in response to Wednesday's attack, which came a year after President Barack Obama declared use of chemical weapons to be a "red line" which would require a firm response. 
 
 Obama has been reluctant to intervene in Syria's 2-1/2-year-old conflict and U.S. officials stressed that he has yet to make a decision on how to respond. A senior senator, Republican Bob Corker, said on Sunday he believed Obama would ask Congress for authorization to use force when lawmakers return from summer recess next month. 
 
 A senior official of the U.S. administration said there was little doubt the Syrian government had gassed its own civilians. 
 
 The White House said Obama and French President Francois Hollande "discussed possible responses by the international community". 
 
 British Prime Minister David Cameron and German Chancellor Angela Merkel agreed that "such an attack demanded a firm response from the international community," Cameron's office said. 
 
 Syria watchers said the government's decision to allow the inspections may have been an attempt to stave off intervention. 
 
 "My view is that the Syrian government's apparent agreement to the U.N. inspection has been triggered by the growing possibility of military action," said Malcolm Chalmers, Research Director at the Britain's Royal United Services Institute. 
 
 "I think that is why they are doing it." 
 
 In London, Foreign Secretary William Hague said evidence of a chemical attack could have already been destroyed by subsequent artillery shelling in the areas or degraded in the days following the strike. 
 
 "We have to be realistic now about what the U.N. team can achieve," he told reporters. 
 
 CEASEFIRE DURING INSPECTIONS 
 
 The United Nations said Damascus had agreed to a ceasefire while the U.N. experts are at the site for inspections. 
 
 Syria confirmed it had agreed to allow access to the inspectors, who arrived in Syria to investigate smaller chemical weapons allegations just three days before the huge incident, which occurred before dawn after a night of heavy bombardment. 
 
 Medicins sans Frontieres says at least 355 people were reported dead in three hospitals from symptoms of poisoning. President Bashar al-Assad's opponents have given death tolls ranging from 500 to well over 1,000. 
 
 The experts' mandate is to find out whether chemical weapons were used, not to assign blame, but the evidence they collect, for example about the missile used, can provide a strong indication about the identity of the party responsible. 
 
 If the U.N. team obtains independent evidence, it could be easier to build an international diplomatic case for intervention. Former weapons investigators say every hour matters. 
 
 The team has been waiting in a Damascus luxury hotel a few miles from the site of what appears to have been the world's worst chemical weapons attack since Saddam Hussein's forces gassed thousands of Iraqi Kurds in 1988. 
 
 Syria's information minister said any U.S. military action would "create a ball of fire that will inflame the Middle East". 
 
 He said Damascus had evidence chemical arms were used by rebels fighting to topple Assad, not by his government. Western states say they believe the rebels lack access to poison gas or weapons that could deliver it. 
 
 Assad's closest ally Iran, repeating Obama's own previous rhetoric, said the United States should not cross a "red line" by attacking Syria. 
 
 Assad ally Russia, which has suggested rebels may have been behind the chemical attack, said it would be a "tragic mistake" to jump to conclusions over who was responsible. 
 
 Two and a half years since the start of a war that has already killed more than 100,000 people, the United States and its allies have yet to take direct action, despite long ago saying Assad must be removed from power. 
 
 (Editing by Mohammad Zargham) ||||| Media playback is unsupported on your device Media caption President Barack Obama: ''I have no interest in any kind of open-ended conflict in Syria'' 
 
 US President Barack Obama has said he has not yet decided on a plan for retaliatory action against Syria. 
 
 But he said he had concluded Syrian government forces were behind a recent chemical weapons attack near Damascus. 
 
 Speaking on US television, Mr Obama said the use of chemical weapons affected US national interests and that sending a "shot across the bows" could have a positive impact on Syria's war. 
 
 His comments follow a day of behind-the-scenes wrangling at the UN. 
 
 The UK had been pushing for permanent members of the UN Security Council to adopt a resolution which would have authorised measures to protect civilians in Syria. 
 
 But Syrian ally Russia refused to agree to the resolution and the meeting produced no end to the diplomatic stalemate which has long characterised the UN position on Syria. 
 
 The US State Department criticised "Russian intransigence" and said it could not allow diplomatic paralysis to serve as a shield for the Syrian leadership. 
 
 Russia is sending an anti-submarine ship and a missile cruiser to the eastern Mediterranean. 
 
 The ships are being sent to strengthen the navy's presence in the area because of the "well-known situation" there, the Russian news agency Interfax has said. 
 
 But another news agency, RIA Novosti, quotes a senior naval command spokesman as saying that this is just a planned rotation, unconnected with Syria. 
 
 'Strong signal' 
 
 Critics have questioned what purpose a limited strike on Syria could serve, but Mr Obama told the Public Broadcasting Service (PBS) it would send the government of Bashar al-Assad "a pretty strong signal that it better not [use chemical weapons] again". 
 
 The US has yet to produce the intelligence it says shows Mr Assad's government is guilty of using chemical weapons, and UN weapons inspectors are still investigating inside Syria. 
 
 The team has just begun a third day of on-site investigations, and UN Secretary General Ban Ki-moon has appealed for it to be "given time to do its job". He said the inspectors would finish their investigations and be out of the area by Saturday morning. 
 
 Syria denies using chemical weapons and blames opposition fighters for the attack near Damascus on 21 August, which reportedly killed hundreds of people. 
 
 If there was action it would be to send the Syrian regime a 'pretty strong signal' 
 
 It accused the West of "inventing" excuses to launch a strike. 
 
 In a sign of growing fears about an impending attack among Syrians, the Associated Press quoted Lebanese officials as saying at least 6,000 Syrians crossed into Lebanon in a 24-hour period through the main Masnaa crossing - compared to a normal daily tally of between 500 and 1,000 refugees. 
 
 "Isn't it enough, all the violence and fighting that we already have in the country, now America wants to bomb us, too?" one 45-year-old woman, entering Lebanon with her five children, told AP. 
 
 In Damascus senior military commanders are reportedly staying away from buildings thought likely to be targeted. You "could hear a pin drop" at one of them, a local resident said. 
 
 'Consequences' 
 
 President Obama told PBS that the US had "not yet made a decision, but the international norm against the use of chemical weapons needs to be kept in place, and hardly anyone disputes that chemical weapons were used in a large scale in Syria against civilian populations". 
 
 Military intervention is morally justified Anthony Luder, Safed, Israel 
 
 Intervening now in Syria would be a terrible mistake Demetrios Nicolaides, Limassol, Cyprus Global readers' voices on Syria 
 
 "We've looked at all the evidence, and we don't believe the opposition possessed chemical weapons of that sort," he said. 
 
 He added he had concluded that the Syrian government carried out the chemical weapons attack. 
 
 "There need to be international consequences, so we are consulting with our allies," he said. 
 
 There was "a prospect that chemical weapons could be directed at us - and we want to make sure that doesn't happen". 
 
 The BBC's David Willis in Washington says Mr Obama looked cautious and spoke in a measured way, and he was clearly concerned about getting Congress on board as well as the American public. 
 
 Opinion polls until now have shown very little interest among the US public in getting involved in the Syrian conflict. 
 
 In an open letter to the president, US House of Representatives Speaker John Boehner demanded he explain "the intended effect of military strikes", and how he would prevent the intervention escalating, if he wanted to win public and congressional backing for action. 
 
 More than 110 members of Congress have signed a letter formally requesting that Mr Obama seek congressional approval for any action in Syria. 
 
 US officials are expected to give senior members of Congress a classified briefing on the evidence that the Syrian government carried out the alleged chemical attack on Thursday. 
 
 Models for possible intervention Iraq 1991: US-led global military coalition, anchored in international law; explicit mandate from UN Security Council to evict Iraqi forces from Kuwait 
 
 US-led global military coalition, anchored in international law; explicit mandate from UN Security Council to evict Iraqi forces from Kuwait Balkans 1990s: US arms supplied to anti-Serb resistance in Croatia and Bosnia in defiance of UN-mandated embargo; later US-led air campaign against Serb paramilitaries. In 1999, US jets provided bulk of 38,000 Nato sorties against Serbia to prevent massacres in Kosovo - legally controversial with UN Security Council resolutions linked to "enforcement measures" 
 
 US arms supplied to anti-Serb resistance in Croatia and Bosnia in defiance of UN-mandated embargo; later US-led air campaign against Serb paramilitaries. In 1999, US jets provided bulk of 38,000 Nato sorties against Serbia to prevent massacres in Kosovo - legally controversial with UN Security Council resolutions linked to "enforcement measures" Somalia 1992-93: UN Security Council authorised creation of international force with aim of facilitating humanitarian supplies as Somali state failed. Gradual US military involvement without clear objective culminated in Black Hawk Down disaster in 1993. US troops pulled out 
 
 UN Security Council authorised creation of international force with aim of facilitating humanitarian supplies as Somali state failed. Gradual US military involvement without clear objective culminated in Black Hawk Down disaster in 1993. US troops pulled out Libya 2011: France and UK sought UN Security Council authorisation for humanitarian operation in Benghazi in 2011. Russia and China abstained but did not veto resolution. Air offensive continued until fall of Gaddafi Syria crisis: Western military options Models for possible intervention Press apprehension as Syria tension builds Syria crisis: Where key countries stand 
 
 The US has said it will not take action alone - but one of its primary allies, the UK, has agreed to wait until UN inspectors report back before taking a parliamentary vote on potential action. 
 
 Russia rejected a UK push to try to agree a resolution on Syria among permanent UN Security Council members on Wednesday, with Foreign Minister Sergei Lavrov saying the UN could not consider any draft resolution or proposed action in Syria before the UN weapons inspectors reported back. 
 
 The use of force without a sanction of the UN Security Council would be a "crude violation" of international law and "lead to the long-term destabilisation of the situation in the country and the region", Mr Lavrov has said. 
 
 UN 'moment' 
 
 The UK, US and France are continuing their discussions following the meeting of the five permanent members. 
 
 The UK will want to be seen to be exhausting every diplomatic avenue, says the BBC's Nick Bryant at the UN headquarters in New York. 
 
 For the UK, there needs to be a UN "moment" - despite the fact that UN action will likely again be blocked by Russia or China. 
 
 But even without UN backing the US and its allies have been clear that they see the military option still open to them, our correspondent says. 
 
 "This is the first use of chemical warfare in the 21st Century," said UK Foreign Secretary William Hague. "It has to be unacceptable... or we will confront even bigger war crimes in the future." 
 
 More than 100,000 people are estimated to have died since the conflict erupted in Syria in March 2011, and the conflict has produced at least 1.7 million refugees. 
 
 Forces which could be used against Syria: ||||| Media playback is unsupported on your device Media caption Defence Secretary Philip Hammond: 'Parliament has spoken' about Syria 
 
 The defence secretary has said MPs could be asked to vote again on action in Syria, but only if circumstances changed "very significantly". 
 
 Labour urged Philip Hammond to "spell out" what would change his mind, after the coalition accepted the defeat of its Commons motion last week. 
 
 But he said it was a "bit rich" of the opposition to "demand" answers, having led protests against military action. 
 
 Meanwhile, the US has delayed strikes pending the approval of Congress. 
 
 Secretary of State John Kerry now says the US has evidence the chemical nerve agent sarin was used by President Bashar al-Assad's government in a deadly attack in Damascus on 21 August. 
 
 The US put the death toll at 1,429, including 426 children. 
 
 Image caption UN weapons inspectors have now left Syria and are analysing their samples 
 
 In other developments: 
 
 A senior UN official says the Syrian refugee situation is the worst displacement crisis of all time, with seven million people estimated to have fled their homes 
 
 A BBC poll suggests nearly three-quarters of Britons believe MPs were right to reject UK military action in Syria - and two thirds did not care if it damaged US-UK relations 
 
 The Ministry of Defence confirms "no UK Armed Forces personnel, including those seconded to work with the armed forces of ally nations, will participate in... military action" against Syria 
 
 France says its intelligence indicates Syria's government carried out the attack, as pressure grows for a parliamentary vote on military action 
 
 Arab League foreign ministers call for "deterrent and necessary measures" against the Assad regime, but Lebanon and Iraq do not back the call 
 
 US ally Jordan rules out joining any coalition against Damascus 
 
 The UK government rejects newspaper claims chemicals exported from Britain could have been used in the production of chemical agents 
 
 US Senator John McCain says a vote by Congress against President Obama's proposal for military force in Syria would be catastrophic 
 
 President Assad denies his forces were behind the attack and warns military intervention would have "negative repercussions" 
 
 Last week, the government lost a Commons vote on supporting action, in principle, against Assad's government by 13 votes. 
 
 Thirty-nine Conservative and Liberal Democrat MPs sided with Labour to bring about the defeat, with several senior ministers since conceding that the question would not be asked again. 
 
 Analysis We now have a people carrier's worth of political heavyweights who didn't like the outcome of last week's Commons vote on Syria musing that perhaps Parliament could be asked to vote again. Lords Howard and Ashdown clambered on board over the weekend, as did Sir Malcolm Rifkind. Now Boris Johnson has joined them. The essence of their case is to test Labour's argument. Ed Miliband didn't rule out military action in principle, so would he change his mind if the evidence changes? But Labour can say this is irrelevant because the prime minister has made it clear the UK won't be involved. Nick Clegg has repeated that the UK will not be involved in military action in response to the use of chemical weapons in Damascus last month. But what would the UK do if there was another chemical weapons attack? 
 
 An ICM poll for the BBC - speaking to 1,000 people by telephone between Friday and Monday - suggested nearly three-quarters of people believed MPs had taken the right decision, and thought it would not harm US-UK relations. 
 
 But the US delay and its claims of fresh evidence against the Syrian regime has prompted suggestions from senior politicians that the House of Commons could reconsider its position. 
 
 Former Lib Dem and Conservative leaders Lord Ashdown and Lord Howard, and former Foreign Secretary Sir Malcolm Rifkind, have said the US's own delay could allow the House of Commons to "think again". 
 
 Conservative London Mayor Boris Johnson also insisted a new proposal "inviting British participation" could still be put before Parliament, 
 
 In the Commons, Labour's shadow defence secretary Jim Murphy asked Mr Hammond to "spell out in what, if any, circumstances" the government would hold a second parliamentary debate on UK military intervention in Syria. 
 
 Mr Hammond replied: "It's a bit rich for you, who last week trooped into the lobbies behind your leader, giving rise to the very situation we now find ourselves in, to demand I tell you precisely in which circumstances we might revisit this issue. 
 
 "I've said already we believe Parliament has spoken clearly on this issue and is unlikely to want to revisit it unless the circumstances change very significantly." 
 
 The BBC's James Landale said Labour sources had cited examples of what would need to change - such as al-Qaeda getting possession of huge stocks of chemical weapons or a direct threat to UK national security emerging - for Parliament to reconsider the matter. 
 
 'Helping al-Qaeda' 
 
 But, questioned at a press conference in London, Deputy Prime Minister Nick Clegg said: "We're not going to go back to Parliament with the same question on the same issue, in response to the same atrocity the week before last, because that decision was made by Parliament." 
 
 Media playback is unsupported on your device Media caption Deputy Prime Minister Nick Clegg says there is no point going back to Parliament over the same question 
 
 The prime minister's official spokesman also told reporters the government had "absolutely no plans to go back to Parliament". 
 
 He said the UK would continue to make the case for a robust response to President Assad at the G20 later this week. 
 
 Meanwhile, Syrian Deputy Foreign Minister Faisal Mekdad told the BBC that any military action against Syria would amount to "support for al-Qaeda and its affiliates", claiming armed groups backed by the US had used chemical weapons - not Syrian troops. 
 
 President Obama's surprise decision to ask Congress for approval means that a strike which was thought to be imminent will now not go ahead before 9 September - when Congress reconvenes - at the earliest. 
 
 The opposition Syrian National Coalition called Mr Obama's decision a "failure of leadership", saying it could "embolden" President Assad's forces. 
 
 More than 100,000 people are estimated to have died since civil conflict erupted in Syria in March 2011. 
 
 The violence began when Syrian security forces clamped down on anti-government protests.
– Syria may have given UN inspectors the OK to access the site of last week's alleged chemical weapons attack, but inspections are not off to a great start. A UN rep confirms that one of the team's vehicles was "deliberately shot at multiple times" by unidentified snipers in Damascus; all are safe. The shooting reportedly occurred in the buffer zone between rebel- and government-controlled territory, and the team will head back to the area once it replaces its vehicle, reports the AP. The Syrian government, for its part, has already blamed "terrorists," reports CNN. More: Once they finally reach the site of last week's alleged attack, UN inspectors will spend two days taking soil, blood, urine, and tissue samples, reports the BBC. But Reuters reports that the US and its allies aren't expecting much: They believe the regime's offer to allow inspectors to the site came too late and any remaining evidence has probably been destroyed by heavy shelling. To wit, a senior White House official dismissed the visit as "too late to be credible." Assad, meanwhile, says that any American attempt at military intervention will be doomed to fail. "Failure awaits the United States as in all previous wars it has unleashed, starting with Vietnam and up to the present day," he said in an interview with a Russian newspaper. UN chief Ban Ki-moon warns that "every hour counts" in determining the facts of what was a "major and terrible incident," reports the Guardian. "We cannot allow impunity in what appears to be a grave crime against humanity," he said. But the UN Security Council, which is split on the issue, has already failed to shoulder its responsibilities and the UK and its allies may have to take action without its approval, Britain's foreign minister says. "Is it possible to respond to chemical weapons without complete unity on the UN Security Council?" William Hague tells the BBC. "I would argue yes it is, otherwise it might be impossible to respond to such outrages."