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 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
– 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."