The US has said it would welcome a plan for Syria to hand over its chemical weapons but expressed scepticism at the Russian initiative, which is designed to avert planned US air attacks.
The US State Department said on Monday it would take a "hard look" at the proposal made by Sergey Lavrov, Russia's foreign minister, that Syria should give its chemical weapons over to international control.
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Russia voiced the plan following a comment made by John Kerry, US secretary of state, in response to a question from a reporter during a press conference in London earlier in the day.
On being asked what could prevent the intervention, Kerry said "he could turn every single bit of his chemical weapons over to the international community" within a week, adding that Assad "isn't about to do it".
Kerry's comments were later clarified as being rhetorical by the State Department, but they set the ball rolling as Russia formalised the idea into a proposal that was welcomed by the UN as well as Walid al-Muallem, Syrian foreign minister.
Muallem's response, however, has not been confirmed by the Syrian government.
Al Jazeera's Patty Culhane, reporting from Washington DC, said the US government had made it clear it was not immediately adopting the proposal, but would look at it carefully.
FSA chief's response
The Russian proposal, and the international reaction to it, brought a sharp response from the commander of the Free Syrian Army, the main Syrian rebel group, Salim Idriss, who accused both the Syrians and the Russians of "deceit".
"We call for strikes and we warn the international community that this regime tells lies, and the liar [Russian President Vladimir] Putin is its teacher. Putin is the biggest liar," Idriss said in an interview to Al Jazeera.
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For his part, Lavrov said Syria, as well as handing over the weapons and having them destroyed, should also become a full member of the Organisation for the Prohibition of Chemical Weapons.
Al Jazeera's Barnaby Phillips, reporting from Moscow, said the Russians were running with Kerry's remark.
"He wasn't bringing a proposal to the press conference, he was responding to a question from a reporter," he said.
"The Russians have picked this up and run with it. It is a new idea and it certainly throws the cards up in the air somewhat."
"All the more, politicians share our estimation that a military solution will lead to an outburst of terrorism both in Syria and in neighbouring countries," Lavrov said on Monday after talks with Muallem.
"The possibility for a political solution remains," he said, emphasising that Muallem had assured him at the talks in Moscow that Syria was still "ready for peace talks".
Ban Ki-moon, the UN secretary-general, said he too welcomed Russia's proposals and called for the creation of UN-supervised zones in Syria where chemical weapons could be destroyed.
"I am considering urging the Security Council to demand the immediate transfer of Syria's chemical weapons and chemical precursor stocks to places inside Syria where they can be safely stored and destroyed," Ban said, adding that the step would overcome the Security Council's "embarrassing paralysis".
Hillary Clinton, the former secretary of state, said any move by Syria to surrender its chemical weapons to international control would be an "important step".
"It is very important to note that this discussion that has taken hold today about potential international control over Syria’s stockpiles only could take place within the context of a credible military threat by the US to keep pressure on the Syrian govt as well as those supporting Syria, such as Russia," she said.
Al Jazeera's Kimberly Halkett, reporting from Washington DC, said the latest developments had not delayed the Senate's vote on military intervemtion, but that there was some doubt that the evidence was as strong as outlined by the government.
"An alternative that had zero support up until now, was one that would allow Assad to sign an international treaty and give him 45 days to do so, saying he won’t use chemical weapons," she said.
"What they're going to do remains a question because they aren't convinced the evidence is there."
Amid the latest diplomatic developments, Harry Reid, the Senate Democratic leader, urged support for planned US military action.
"Sitting on the sidelines isn't what made the United States of America the greatest nation in the world in years past and ... sitting on the sidelines won't make us a better nation tomorrow," he said.
Obama and aides have refused to speculate about what he would do if Congress votes no.