In Congress, a planned vote in the Democrat-controlled Senate on whether to authorise military action was shelved until further notice. In the Republican-controlled House of Representatives, some members said they did not expect a vote at all.
President Barack Obama made the case for action in Syria directly to a deeply sceptical American public, arguing in a prime-time address that the US must be prepared to shoulder "the burdens of leadership".
Obama said the Russian initiative, as well as the Assad regime's offer to join a treaty banning the use of chemical weapons, were "encouraging signs". Although cautioning that it was "too early to tell whether this offer will succeed", Obama said the initiative had "the potential to remove the threat of chemical weapons without the use of force".
"I have therefore asked the leaders of Congress to postpone a vote to authorise the use of force while we pursue this diplomatic path."
He did not acknowledge surveys of members of Congress which show him likely to suffer a humiliating defeat if he attempted to secure the backing of the House of Representatives.
The President made no ultimatums to Bashar al-Assad, nor did he set any specific timetable on how quickly Syria would need to prove its offer was credible in order to avoid strikes. However, he warned: "I've ordered our military to maintain their current posture, to keep the pressure on Assad and to be in a position to respond if diplomacy fails."
Vladimir Putin, the Russian President, opened a rift with the US by saying that the idea would work only "if we hear that the American side and all those who support the United States in this sense reject the use of force".
Syria's regime, which has more than 1000 tonnes of poison gas, according to the French Government, promised to co-operate with the Russian proposal. Walid al-Muallem, the Syrian Foreign Minister, said the country was willing to sign up to the Chemical Weapons Convention.
France has drawn up a tough resolution which blames Syria's regime for the poison gas attacks in Damascus on August 21 and demands the surrender of all chemical weapons. Otherwise, Syria would face "severe consequences" under Chapter VII of the UN Charter - armed force.
But the Security Council has failed to pass any resolutions on Syria since the onset of the civil war in 2011. Russia has twice used its veto to protect Assad. This sequence appeared to be repeating itself when Sergei Lavrov, the Russian Foreign Minister, called the French draft "unacceptable". If no agreement is possible in the Security Council, then the Russian plan could fall by the wayside very quickly.
The sequence of events that brought America back from the brink of war may not have been as spontaneous as they first appeared.
Margaret Brennan of CBS News, who asked Kerry if there was anything the Syrians could do to avert American bombing, later disclosed that the notion of Syria yielding its chemical weapons had been discussed by US and Russian officials in May.
The countries' presidents spoke privately by telephone early in that month, while the Secretary of State met Lavrov, twice.
Obama told his US interviewers that he had discussed the idea of a chemical weapons surrender with Putin last week at an impromptu 20-minute meeting at the G20 summit in St Petersburg. The Russians, likewise, said the suggestion was "definitely discussed" between the two leaders at the G20.
The idea of presenting such a demand to Damascus had been floated publicly for the first time during the weekend at the end of a European Union foreign ministers' conference in Lithuania that was addressed by Kerry.
Chris Doyle, director of the Council for Arab-British Understanding, said: "I don't believe this was purely a gaffe by Kerry. It sounds infinitely plausible that this had been discussed previously, but you could argue the Russians wanted to hear Kerry say something in public before they made a diplomatic move.
"It makes sense because a delay suits both sides."
