President Barack Obama said a Russian plan to head off threatened US strikes on Syria by securing a deal to destroy the regime's chemical weapons could be a "significant breakthrough."
Obama warned Monday he had not taken military strikes off the table but, in agreeing to consider the Russian initiative, he effectively pushed back the timetable for possible action.
The US leader had intended to spend the day selling his plan to launch punitive military strikes against Bashar al-Assad's regime to skeptical American voters and lawmakers.
Instead, he found himself responding to a surprise Russian diplomatic initiative which would see Assad's stockpile of banned chemical arms taken under international control.
Iran's foreign ministry spokeswoman also welcomed Russia's plan.
Marzieh Afgham told a media conference in Tehran that the proposal should include the destruction of chemical weapons in the hands of rebel groups fighting to topple the regime of Syrian President Bashar al-Assad.
"The Islamic republic of Iran favourably welcomes the (Russian) initiative which aims at halting all military action" against Syria, Afgham said.
Obama, who faces a tough task winning Congressional approval for even a limited military action, admitted that US lawmakers were not close to voting on the issue.
"I don't anticipate that you would see a succession of votes this week or anytime in the immediate future," he told ABC news.
And, in a series of television interviews, he insisted it had only come about because Assad and his allies in Moscow could see the United States was serious about using force.
"I think what we're seeing is that a credible threat of a military strike from the United States, supported potentially by a number of other countries around the world, has given them pause and makes them consider whether or not they would make this move," he told NBC.
"And if they do, then this could potentially be a significant breakthrough. But we have to be skeptical because this is not how we've seen them operate over the last couple of years."
In separate interviews with several US broadcasters, Obama said he had discussed the issue with Russia's President Vladimir Putin at last week's G20 summit in Saint Petersburg.
Washington's European allies gave a similarly cautious welcome to the plan, and UN Secretary General Ban Ki-moon issued his own plea for a mission to secure and dispose of the weapons.
Russian Foreign Minister Sergei Lavrov had met his Syrian counterpart and urged Damascus to "place chemical weapons under international control and then to have them destroyed."
Speaking in Moscow, Syria's Foreign Minster Walid al-Muallem welcomed the Russian move, though it was not immediately clear if a still defiant Assad would agree to the measure.
The rebels battling Assad, who hoped to see US missiles rain down on the regime, denounced the idea as a plot by Putin to protect Assad.
Britain's Prime Minister David Cameron also expressed concern that the plan might be "a distraction tactic" but broadly welcomed it.
German Chancellor Angela Merkel described the Kremlin's proposal as "interesting" but added that she hoped it would be put into place quickly and not simply be used to "buy time."
Signup to our newsletter and follow us on Facebook and Twitter!
And France, the only Western ally to have offered to take part in a US-led strike, said Assad must commit "without delay" to the elimination of his chemical arsenal.
United Nations leader Ban, meanwhile, called for the creation of UN supervised zones in Syria where the country's chemical weapons can be destroyed.
He told reporters he may propose the zones to the Security Council if UN inspectors confirm banned weapons were used and to overcome the council's "embarrassing paralysis" over Syria.
For his part, Assad warned earlier in an interview with US television that the United States will "pay the price" if it attacks Syria.
While Obama portrayed Russia's idea as a victory for Washington's policy of threatening military action, it still leaves him in a domestic political bind.
Having chosen to seek Congressional support for a limited US military strike against Syria, he could be defeated on his home turf.
Senate Majority Leader Harry Reid said he would delay a key procedural vote on authorizing force until after Obama makes a national address on the issue on Tuesday.
"I wouldn't say I'm confident," Obama said of the prospect of his winning the impending votes.
Opposition is strong to a measure that is opposed by a majority of US voters, weary of war after drawn out, bloody and inconclusive American missions in Iraq and Afghanistan.
A New York Times/CBS poll late Monday said 62 percent of people surveyed said the United States should not take a leading role in trying to solve foreign conflicts.
The lower house of the US Congress, the House of Representatives, is led by Republicans who oppose Obama's every move.
Some anti-war Democrats are also expected to oppose the motion, and the support of pro-war neo-conservatives in the Republican ranks may not be enough to push it through.
But US cruise missile destroyers are idling in the eastern Mediterranean, preparing for what American officials described as a limited punitive strike.
According to US intelligence, on August 21 a chemical attack against rebel-held suburbs of Damascus killed more than 1,400 people, including 400 children gassed in their beds.
Western states and the Arab League have condemned the alleged barrage as a war crime and blamed it on Assad's regime.
US-based rights group Human Rights Watch said in a statement early Tuesday that all available evidence "strongly suggested" the Syrian government forces were responsible for the attack.
Human Rights Watch issued its findings in a 22-page report after analyzing witness accounts of the rocket attacks, the physical remnants of weapons used and the symptoms exhibited by the victims.
Obama has argued that a military strike is necessary to defend the long-established international taboo against the use of chemical weapons.
He has refused to rule out acting alone, with neither congressional nor international support, but a political defeat at home would be a blow to his credibility and strengthen Assad's hand.
The crisis in Syria flared after Assad's forces launched a brutal crackdown on peaceful anti-regime protests that began in March 2011, and eventually degenerated into an all-out civil war that has killed more than 100,000 people, according to the UN.