Barack Obama has said a proposal to put Syria's chemical weapons under international control to avoid US military strikes could be a potential breakthrough.
But he said he would prefer to have a diplomatic solution to the crisis rather than launch a military attack and called it "a potentially positive development".
US secretary of state John Kerry earlier suggested that Syria could avoid a potential US air attack by putting its chemical weapons under international control. Syria's ally Russia quickly took the idea to Syria's foreign minister, who said Damascus welcomed the proposal.
The public proposal from Russia followed what seemed to be an offhand remark by Mr Kerry. Mr Obama told PBS' NewsHour that he and Mr Putin did speak about it last week while Mr Obama was in St Petersburg, Russia, for the G20 economic summit. The two leaders had an impromptu chat on Friday for about 20 minutes. Mr Obama said it was a continuation of previous conversations he had with Mr Putin about securing Syria's chemical weapons.
Meanwhile, the US Senate is delaying a test vote on authorising US military strikes against Syria. Senate Majority Leader Harry Reid said it would not be beneficial to hold the vote while international discussions continue regarding Syria's use of chemical weapons. Mr Reid's action comes amid increased opposition in the Senate to US military intervention in Syria. The Nevada Democrat had planned a full Senate vote on Wednesday. It is unclear when that might happen now.
Mr Obama conceded he might lose his fight for congressional support of a military strike against Syria and declined to say what he would do if politicians reject his call to back retaliation for the August 21 chemical weapons attack. "I think it's fair to say that I haven't decided" on a next step if congress turns its back, the president said in an NBC interview, one of six he granted during the day as part of a furious lobbying campaign aimed at winning support from dubious politicians as well as a war-weary public.
Speaking of the government of Bashar Assad, he said the credible threat of a military strike led by the United States "has given them pause and makes them consider whether or not they could make this move" to surrender control of their chemical weapons stockpile.
Public opinion polling was daunting for the president and his team. An Associated Press poll showed that 61% of those surveyed want congress to vote against authorisation of US military strikes in Syria and 26% want politicians to support such an action, with the remainder undecided.