Media playback is unsupported on your device Media caption Obama statement 
 
 Russian President Vladimir Putin has challenged the US to present to the UN evidence that Syria attacked rebels with chemical weapons near Damascus. 
 
 Mr Putin said it would be "utter nonsense" for Syria's government to provoke opponents with such attacks. 
 
 US President Barack Obama says he is considering military action against Syria after intelligence reports that 1,429 people were killed on 21 August. 
 
 UN weapons inspectors have now left Syria and arrived in the Netherlands. 
 
 They are taking the evidence they gathered during four days of site visits to the Organisation for the Prevention of Chemical Weapons, in The Hague. 
 
 Media playback is unsupported on your device Media caption The BBC's security correspondent Frank Gardner examines what we know about the Syria attack on 21 August 
 
 The samples are thought to include soil, swabs from munitions, blood and hair from the victims and, experts say, possibly even flesh from dead bodies. 
 
 The UN has said its inspectors had been able to carry out a "wide range of fact-finding activities". However, their mandate is limited to determining the use of chemical weapons and not who used them. 
 
 UN spokesman Martin Nesirky refused to set a timeframe for the results of lab tests and the inspectors' full report. 
 
 He described as "grotesque" the suggestion that the departure of inspectors from Syria "somehow opens the window for military action". 
 
 The UN's humanitarian work in Syria would continue, he said. 
 
 Obama statement 
 
 The US says hundreds of children were among those killed in the suspected chemical weapons attacks, which it blames on the Syrian government. 
 
 Syria says the US claim is "full of lies" and says rebels carried out the attacks. 
 
 Mr Obama is to make a statement on Syria at 17:15 GMT but will not announce any imminent military action, the White House says. 
 
 Senior officials are holding conference calls on Saturday about Syria with both Republican and Democratic senators. 
 
 Mr Obama said on Friday the US was planning a "limited, narrow" military response that would not involve "boots on the ground". 
 
 'Trump card' 
 
 The inspectors' departure from Syria removes both a practical and a political obstacle to the launch of US-led military action, correspondents say. 
 
 At the scene There are those in Syria who will cheer on the US action and those who will be quite worried by it, but I think everyone is making some preparation. People are trying to buy what they can, stockpile things, get water, bread, food that lasts, because they don't know what's going to happen. They don't know what President Obama means by a limited attack and what consequences that may have for their lives and the degree to which it would stay limited. Damascus holds its breath 
 
 The BBC's Jeremy Bowen in Damascus says people are worried and are making preparations. 
 
 They do not know what Mr Obama meant by a limited attack and what consequences it will have, he adds. 
 
 Speaking to journalists in the Russian far-eastern city of Vladivostok, Mr Putin urged Mr Obama - as a Nobel Peace Prize laureate - to think about future victims in Syria before using force. 
 
 He said it was ridiculous to suggest the Syrian government was to blame for the attack, calling it a "provocation by those who want to drag other countries into the Syrian conflict". 
 
 "Syrian government troops are on the offensive and have surrounded the opposition in several regions," he said. 
 
 "In these conditions, to give a trump card to those who are calling for a military intervention is utter nonsense." 
 
 Media playback is unsupported on your device Media caption Russia's Vladimir Putin challenges US on Syria claims 
 
 He said that the US failure to present evidence to the international community was "simply disrespectful". 
 
 "If there is evidence it should be shown. If it is not shown, then there isn't any," he said. 
 
 The main findings of the unclassified US evidence state that: 
 
 the attack killed 1,429 people, including 426 children 
 
 Syrian military chemical weapons personnel were operating in the area in the three days before the attack 
 
 Satellite evidence shows rockets launched from government-held areas 90 minutes before the first report of chemical attack 
 
 100 videos attributed to the attack show symptoms consistent with exposure to a nerve agent 
 
 Communications were intercepted involving a senior Damascus official who "confirmed chemical weapons were used" and was concerned about UN inspectors obtaining evidence 
 
 'Completely unexpected' 
 
 Russia - a key ally of Syria - has previously warned that "any unilateral military action bypassing the UN Security Council" would be a "direct violation of international law". 
 
 Moscow, along with China, has vetoed two previous draft resolutions on Syria. 
 
 Media playback is unsupported on your device Media caption Barack Obama: "We're not considering any boots on the ground approach" 
 
 Mr Putin also expressed surprise at a vote in the British parliament on Thursday ruling out participation in military action. 
 
 "I will be honest: this was completely unexpected for me," he said. 
 
 "This shows that in Great Britain, even if it is the USA's main geopolitical ally in the world... there are people who are guided by national interests and common sense, and value their sovereignty." 
 
 Meanwhile in France - seen as the main US ally since the UK vote - an opinion poll suggested that 64% opposed the use of force. 
 
 Neither France nor the US needs parliamentary approval for military action. 
 
 Syrian President Bashar al-Assad has said his country will defend itself against any Western "aggression". 
 
 Forces which could be used against Syria: 
 
 •Four US destroyers - USS Gravely, USS Ramage, USS Barry and USS Mahan - are in the eastern Mediterranean, equipped with cruise missiles. The missiles can also be fired from submarines, but the US Navy does not reveal their locations 
 
 •Airbases at Incirlik and Izmir in Turkey, and in Jordan, could be used to carry out strikes 
 
 •Two aircraft carriers - USS Nimitz and USS Harry S Truman are in the wider region 
 
 •French aircraft carrier Charles de Gaulle is currently in Toulon in the western Mediterranean 
 
 •French Rafale and Mirage aircraft can also operate from Al-Dhahra airbase in the UAE ||||| Image caption The UN team spoke to witnesses and survivors in Muadhamiya 
 
 Russia and China have stepped up their warnings against military intervention in Syria, with Moscow saying any such action would have "catastrophic consequences" for the region. 
 
 The US and its allies are considering launching strikes on Syria in response to deadly attacks last week. 
 
 The US said there was "undeniable" proof of a chemical attack, on Monday. 
 
 UN chemical weapons inspectors are due to start a second day of investigations in the suburbs of Damascus. 
 
 The UN team came under sniper fire as they tried to visit an area west of the city on Monday. 
 
 A spokesman for UK Prime Minister David Cameron says the UK is making contingency plans for military action in Syria. 
 
 Mr Cameron has cut short his holiday and returned to London to deal with the Syrian crisis. 
 
 The administration has deliberately left itself almost no room for manoeuvre - its credibility would now be zero if it failed to take some form of military action How Syria conflict affects neighbours 
 
 Russian foreign ministry spokesman Alexander Lukashevich has called on the international community to show "prudence" over the crisis and observe international law. 
 
 "Attempts to bypass the Security Council, once again to create artificial groundless excuses for a military intervention in the region are fraught with new suffering in Syria and catastrophic consequences for other countries of the Middle East and North Africa," he said in a statement. 
 
 Late on Monday, the US said it was postponing a meeting on Syria with Russian diplomats, citing "ongoing consultations" about alleged use of chemical weapons in Syria. 
 
 Hours later, Russia expressed regret about the decision. The two sides had been due to meet in The Hague on Wednesday to discuss setting up an international conference on finding a political solution to the crisis. 
 
 The Russian deputy defence minister, Gennady Gatilov said working out the political parameters for a resolution on Syria would be especially useful, with the threat of force hanging over the country. 
 
 Image caption UN chemical weapons inspectors spent nearly three hours in the suburb of Muadhamiya in western Damascus on Monday. Image caption The inspectors visited two hospitals and interviewed survivors, eyewitnesses and doctors over last week's suspected chemical attack near the Syrian capital. Image caption Amateur video was posted online apparently showing a UN inspector measuring and photographing a canister. previous slide next slide 
 
 On Monday, Mr Cameron spoke to Russian President Vladimir Putin who said there was no evidence yet that Syria had used chemical weapons against rebels, Mr Cameron's office said. 
 
 The official Chinese news agency, Xinhua, said Western powers were rushing to conclusions about who may have used chemical weapons in Syria before UN inspectors had completed their investigation. 
 
 UN visit 
 
 Both the Syrian government and rebels have blamed each other for last Wednesday's attacks. 
 
 Medical charity Medecins Sans Frontieres said three hospitals it supported in the Damascus area had treated about 3,600 patients with "neurotoxic symptoms", of whom 355 had died. 
 
 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 Models for possible intervention 
 
 US officials said there was "little doubt" that President Bashar al-Assad's government was to blame. 
 
 UN inspectors spent nearly three hours in the western district of Muadhamiya on Monday where they visited two hospitals and interviewed survivors, eyewitnesses and doctors. 
 
 A UN spokesman said they had collected some samples. 
 
 Earlier in the day, the UN convoy came under fire from unidentified snipers and was forced to turn back before resuming its journey. 
 
 UN Secretary General Ban Ki-moon condemned the shooting and asked the UN team in Syria to register a complaint. 
 
 'Accountability' 
 
 In the most forceful US reaction yet, US Secretary of State John Kerry on Monday described the recent attacks in the Damascus area as a "moral obscenity". 
 
 He said the delay in allowing UN inspectors to the sites was a sign the Syrian government had something to hide. 
 
 He said Washington had additional information about the attacks that it would make public in the days ahead. 
 
 "What we saw in Syria last week should shock the conscience of the world. It defies any code of morality," Mr Kerry said at a news conference on Monday. 
 
 "Make no mistake, President Obama believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people." 
 
 Media playback is unsupported on your device Media caption John Kerry: "There is a clear reason that the world has banned entirely the use of chemical weapons" 
 
 Washington has recently bolstered its naval presence in the eastern Mediterranean and military leaders from the US, UK and their allies have convened a meeting in Jordan. 
 
 Analysts believe the most likely US action would be sea-launched cruise missiles targeting Syrian military installations. 
 
 But Russian Foreign Minister Sergei Lavrov told reporters on Monday the West had not produced any proof that President Assad's forces had used chemical weapons. 
 
 He was responding to suggestions from some Western countries that military action against the Syrian government could be taken without a UN mandate. 
 
 Mr Lavrov said the use of force without Security Council backing would be "a crude violation of international law". 
 
 Earlier, UK Foreign Secretary William Hague told the BBC an international military response to the suspected use of chemical weapons would be possible without the backing of the UN. 
 
 The UN Security Council is divided, with Russia and China opposing military intervention and the UK and France warning that the UN could be bypassed if there was "great humanitarian need". 
 
 In a column in The Times newspaper, former UK PM Tony Blair has written that if the West does not intervene to support freedom and democracy in Egypt and Syria, the Middle East will face catastrophe 
 
 The UN says more than 100,000 people have been killed since the uprising against President Assad began more than two years ago. The conflict has produced more than 1.7 million registered refugees.
– John Kerry says he has "high confidence" in US intelligence reports that Syria used chemical weapons. Vladimir Putin has two much different words on the subject: "utter nonsense." The Russian leader used the phrase in urging the US to hold off on any military action until the UN has completed its investigation, reports the BBC. The clock is ticking on that: UN inspectors left Syria today and will brief Secretary-General Ban Ki-moon, but their full report to the Security Council might take a week or so to complete, reports CNN. Kerry and Obama have suggested that the US won't wait that long, in part because the UN inspectors are charged only with determining whether chemical weapons were used, not who employed them. The US says it already is sure that Bashar al-Assad is the culprit. Putin, though, told reporters that it would have been foolish for Assad to order the Aug. 21 attack because his troops have the upper hand in the war. "In these conditions, to give a trump card to those who are calling for a military intervention is utter nonsense."