The administration pressed ahead in its efforts to persuade Congress to authorize a military strike, and Obama said the day's developments were doubtless due in part to the "credible possibility" of that action. He stuck to his plan to address the nation Tuesday night, while the Senate Democratic leader postponed a vote on authorization.
The sudden developments broke into the open when Russia's foreign minister, seizing on what appeared at the time to be an off-the-cuff remark by Secretary of State John Kerry, appeared in Moscow alongside his Syrian counterpart and proposed the chemical weapons turnover and destruction. The Syrian quickly embraced the idea, and before long U.N. Secretary-General Ban Ki-moon did, too.
Obama, who appeared Monday evening in interviews on six TV networks, said the idea actually had been broached in his 20-minute meeting with Russian President Vladimir Putin last week on the sidelines of an economic summit in St. Petersburg, Russia. Obama said he directed Kerry to have more conversations with the Russians and "run this to ground."
The president said he would "absolutely" halt a U.S. military strike if Syria's stockpiles were successfully secured, though he remained skeptical about Assad's willingness to carry out the steps needed.
"My objective here has always been to deal with a very specific problem," Obama said in an interview with ABC News. "If we can do that without a military strike, that is overwhelmingly my preference."
He cast Russia's proposal as a direct result of the pressure being felt by Syria because of the threat of a U.S. strike and warned that he would not allow the idea to be used as a stalling tactic.
"I don't think that we would have gotten to this point unless we had maintained a credible possibility of a military strike, and I don't think now is the time for us to let up on that," he said.
Still, the White House has had scant success in persuading members of Congress - including Democrats - to support the idea of military action. Senators continued to announce their opposition through the day.
The proposal from Russian Foreign Minister Sergey Lavrov came just hours after Kerry told reporters in London that Assad could avoid a U.S. attack and resolve the crisis surrounding the use of chemical weapons by surrendering control of "every single bit" of his arsenal to the international community by the end of the week.
The State Department sought to tamp down the potential impact of Kerry's comments by calling them a "rhetorical" response to a hypothetical question and not "a proposal." But their importance became more clear as the day progressed.
Kerry spoke by phone with Lavrov shortly after making his comments in London, and officials familiar with the call said Lavrov had told Kerry that he had seen the remarks and would be issuing a public statement. Kerry told Lavrov that his comments were not a proposal but the U.S. would be willing to review a serious plan, the officials said. They stressed that he made clear that Lavrov could not present the idea as a joint U.S.-Russian proposal.
The officials commented only on condition of anonymity because they were not authorized to describe the information publicly.
British Prime Minister David Cameron said the proposal was worth exploring, the French foreign ministry said it deserved close examination and former Secretary of State Hillary Rodham Clinton said any move by Syria to surrender its chemical weapons would be an "important step." Clinton, in contrast with the White House and State Department, credited Kerry and Russia jointly for the proposal.
Obama still faces a decidedly uphill fight to win congressional authorization for the use of force - and serious doubts by the American public - and Monday's developments, planned or not, could provide him with a way out of a messy political and foreign policy bind.
The U.S. accuses Assad's government of being behind an attack using sarin gas in a Damascus suburb on Aug. 21, killing 1,429 people. Some other estimates of the deaths are lower, but there is wide agreement that chemical weapons were used. Experts believe that the Syrian government's arsenal of chemical weapons includes nerve agents like sarin, tabun and VX as well as mustard gas.
In an interview with Charlie Rose that was broadcast Monday on "CBS This Morning," Assad denied responsibility for the Aug. 21 attack, accused the Obama administration of spreading lies without providing a "single shred of evidence," and warned that air strikes against his nation could bring retaliation. Pressed on what that might include, Assad responded, "I'm not fortune teller."
Later Monday, Syria's foreign minister, meeting with his Russian counterpart in Moscow, addressed the idea of getting rid of any chemical weapons.
"Syria welcomes the Russian proposal out of concern for the lives of the Syrian people, the security of our country and because it believes in the wisdom of the Russian leadership that seeks to avert American aggression against our people," said al-Moallem.
Kerry's comments came at a news conference with British Foreign Secretary William Hague and in response to a question about what, if anything, Assad could do to stop the U.S. from punishing it for the use of chemical weapons.
"Sure," Kerry replied. "He could turn over every single bit of his chemical weapons to the international community in the next week. Turn it over, all of it, without delay, and allow a full and total accounting for that. But he isn't about to do it, and it can't be done, obviously."
Traveling with Kerry, State Department spokeswoman Jen Psaki tried to blunt the suggestion.
"Secretary Kerry was making a rhetorical argument about the impossibility and unlikelihood of Assad turning over chemical weapons he has denied he used," she said. "His point was that this brutal dictator with a history of playing fast and loose with the facts cannot be trusted to turn over chemical weapons otherwise he would have done so long ago."
And, in a speech, Obama's national security adviser Susan Rice reiterated that the president had decided it is in U.S. interests to carry out limited strikes.
Al-Moallem and Lavrov had not reacted to Kerry's comments when they spoke to reporters immediately after their meeting. But Lavrov appeared before television cameras several hours later to say Moscow would urge Syria to quickly place its chemical weapons under international control and then dismantle them.
"If the establishment of international control over chemical weapons in that country would allow avoiding strikes, we will immediately start working with Damascus," Lavrov said.
"We are calling on the Syrian leadership to not only agree on placing chemical weapons storage sites under international control, but also on its subsequent destruction and fully joining the treaty on prohibition of chemical weapons," he said.
Russia's proposal provided confirmation from Syria's most important international ally that the Syrian government possesses chemical weapons, and al-Moallem's welcome was a tacit acknowledgment. Syria's foreign ministry last year retracted a threat to use chemical weapons, saying it was not acknowledging that it had them.
Associated Press writers Vladimir Isachenkov in Moscow, Zeina Karam in Beirut, Connie Cass in Washington, Deb Riechmann in London and Edith Lederer at the U.N. contributed to this report.