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 ||||| Story highlights Syrian official: Obama climbed to the top of the tree, "doesn't know how to get down" 
 
 Obama sends a letter to the heads of the House and Senate 
 
 Obama to seek congressional approval on military action against Syria 
 
 Aim is to determine whether CW were used, not by whom, says U.N. spokesman 
 
 It's official: U.S. President Barack Obama wants lawmakers to weigh in on whether to use military force in Syria. 
 
 Obama sent a letter to the heads of the House and Senate on Saturday night, hours after announcing that he believes military action against Syrian targets is the right step to take over the alleged use of chemical weapons. 
 
 The proposed legislation from Obama asks Congress to approve the use of military force "to deter, disrupt, prevent and degrade the potential for future uses of chemical weapons or other weapons of mass destruction." 
 
 It's a step that is set to turn an international crisis into a fierce domestic political battle 
 
 There are key questions looming over the debate: What did U.N. weapons inspectors find in Syria? What happens if Congress votes no? And how will the Syrian government react? 
 
 In a televised address from the White House Rose Garden earlier Saturday, the president said he would take his case to Congress, not because he has to -- but because he wants to. 
 
 "While I believe I have the authority to carry out this military action without specific congressional authorization, I know that the country will be stronger if we take this course, and our actions will be even more effective," he said. "We should have this debate, because the issues are too big for business as usual." 
 
 Obama said top congressional leaders had agreed to schedule a debate when the body returns to Washington on September 9. The Senate Foreign Relations Committee will hold a hearing over the matter on Tuesday, Sen. Robert Menendez said. 
 
 U.N. inspectors leave Syria 
 
 Obama's remarks came shortly after U.N. inspectors left Syria, carrying evidence that will determine whether chemical weapons were used in an attack early last week in a Damascus suburb. 
 
 "The aim of the game here, the mandate, is very clear -- and that is to ascertain whether chemical weapons were used -- and not by whom," U.N. spokesman Martin Nesirky told reporters on Saturday. 
 
 But who used the weapons in the reported toxic gas attack in a Damascus suburb on August 21 has been a key point of global debate over the Syrian crisis. 
 
 Top U.S. officials have said there's no doubt that the Syrian government was behind it, while Syrian officials have denied responsibility and blamed jihadists fighting with the rebels. 
 
 British and U.S. intelligence reports say the attack involved chemical weapons, but U.N. officials have stressed the importance of waiting for an official report from inspectors. 
 
 The inspectors will share their findings with U.N. Secretary-General Ban Ki-moon Ban, who has said he wants to wait until the U.N. team's final report is completed before presenting it to the U.N. Security Council. 
 
 The Organization for the Prohibition of Chemical Weapons, which nine of the inspectors belong to, said Saturday that it could take up to three weeks to analyze the evidence they collected. 
 
 "It needs time to be able to analyze the information and the samples," Nesirky said. 
 
 He noted that Ban has repeatedly said there is no alternative to a political solution to the crisis in Syria, and that "a military solution is not an option." 
 
 Obama: 'This menace must be confronted' 
 
 Obama's senior advisers have debated the next steps to take, and the president's comments Saturday came amid mounting political pressure over the situation in Syria. Some U.S. lawmakers have called for immediate action while others warn of stepping into what could become a quagmire. 
 
 Some global leaders have expressed support, but the British Parliament's vote against military action earlier this week was a blow to Obama's hopes of getting strong backing from key NATO allies. 
 
 On Saturday, Obama proposed what he said would be a limited military action against Syrian President Bashar al-Assad. Any military attack would not be open-ended or include U.S. ground forces, he said. 
 
 Syria's alleged use of chemical weapons earlier this month "is an assault on human dignity," the president said. 
 
 A failure to respond with force, Obama argued, "could lead to escalating use of chemical weapons or their proliferation to terrorist groups who would do our people harm. In a world with many dangers, this menace must be confronted." 
 
 Obama decision came Friday night 
 
 What will happen if they vote no? 
 
 It's unclear. A senior administration official told CNN that Obama has the authority to act without Congress -- even if Congress rejects his request for authorization to use force. 
 
 Obama on Saturday continued to shore up support for a strike on the al-Assad government. 
 
 He spoke by phone with French President Francois Hollande before his Rose Garden speech. 
 
 "The two leaders agreed that the international community must deliver a resolute message to the Assad regime -- and others who would consider using chemical weapons -- that these crimes are unacceptable and those who violate this international norm will be held accountable by the world," the White House said. 
 
 Meanwhile, as uncertainty loomed over how Congress would weigh in, U.S. military officials said they remained at the ready. 
 
 Reactions mixed to Obama's speech 
 
 A spokesman for the Syrian National Coalition said that the opposition group was disappointed by Obama's announcement. 
 
 "Our fear now is that the lack of action could embolden the regime and they repeat his attacks in a more serious way," said spokesman Louay Safi. "So we are quite concerned." 
 
 Some members of Congress applauded Obama's decision. 
 
 House Speaker John Boehner, Majority Leader Eric Cantor, Majority Whip Kevin McCarthy and Conference Chair Cathy McMorris Rodgers issued a statement Saturday praising the president. 
 
 "Under the Constitution, the responsibility to declare war lies with Congress," the Republican lawmakers said. "We are glad the president is seeking authorization for any military action in Syria in response to serious, substantive questions being raised." 
 
 More than 160 legislators, including 63 of Obama's fellow Democrats, had signed letters calling for either a vote or at least a "full debate" before any U.S. action. 
 
 British Prime Minister David Cameron, whose own attempt to get lawmakers in his country to support military action in Syria failed earlier this week, responded to Obama's speech in a Twitter post Saturday. 
 
 "I understand and support Barack Obama's position on Syria," Cameron said. 
 
 An influential lawmaker in Russia -- which has stood by Syria and criticized the United States -- had his own theory. 
 
 "The main reason Obama is turning to the Congress: the military operation did not get enough support either in the world, among allies of the US or in the United States itself," Alexei Pushkov, chairman of the international-affairs committee of the Russian State Duma, said in a Twitter post. 
 
 In the United States, scattered groups of anti-war protesters around the country took to the streets Saturday. 
 
 "Like many other Americans...we're just tired of the United States getting involved and invading and bombing other countries," said Robin Rosecrans, who was among hundreds at a Los Angeles demonstration. 
 
 Syria's government unfazed 
 
 After Obama's speech, a military and political analyst on Syrian state TV said Obama is "embarrassed" that Russia opposes military action against Syria, is "crying for help" for someone to come to his rescue and is facing two defeats -- on the political and military levels. 
 
 Syria's prime minister appeared unfazed by the saber-rattling. 
 
 "The Syrian Army's status is on maximum readiness and fingers are on the trigger to confront all challenges," Wael Nader al-Halqi said during a meeting with a delegation of Syrian expatriates from Italy, according to a banner on Syria State TV that was broadcast prior to Obama's address. 
 
 An anchor on Syrian state television said Obama "appeared to be preparing for an aggression on Syria based on repeated lies." 
 
 A top Syrian diplomat told the state television network that Obama was facing pressure to take military action from Israel, Turkey, some Arabs and right-wing extremists in the United States. 
 
 "I think he has done well by doing what Cameron did in terms of taking the issue to Parliament," said Bashar Jaafari, Syria's ambassador to the United Nations. 
 
 Both Obama and Cameron, he said, "climbed to the top of the tree and don't know how to get down." 
 
 The Syrian government has denied that it used chemical weapons in the August 21 attack, saying that jihadists fighting with the rebels used them in an effort to turn global sentiments against it. 
 
 British intelligence had put the number of people killed in the attack at more than 350. 
 
 On Saturday, Obama said "all told, well over 1,000 people were murdered." U.S. Secretary of State John Kerry on Friday cited a death toll of 1,429, more than 400 of them children. No explanation was offered for the discrepancy.
– 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."