The United States tonight welcomed a Russian admission that Syria's rebels may succeed in their drive to topple President Bashar al-Assad.
The US called on Moscow to join efforts to manage a peaceful political transition.
"We want to commend the Russian government for finally waking up to the reality and acknowledging that the regime's days are numbered," State Department spokeswoman Victoria Nuland told a news briefing.
"The question now is, will the Russian government join those of us in the international community who are working with the opposition to try to have a smooth democratic transition?"
Another US official said the rebels appeared to be making gains against Mr Assad and his forces.
"The rebels are pressuring Assad harder than ever before and his reach is contracting," the US official said on condition of anonymity.
"Assad probably still believes that Syria is his and illusions can die hard. But Assad and those closest to him have got to be feeling the psychological strain of fighting a long war that is not going their way," the official said.
Russian Deputy Foreign Minister Mikhail Bogdanov, the Kremlin's envoy for the Middle East, said today that rebel gains on the ground mean that their ultimate victory over Assad "cannot be ruled out".
Mr Bogdanov's comments were among the most pessimistic yet from Russia, which has shielded Assad's government from UN Security Council censure and sanctions, resisting Western pressure to join efforts to push him from power.
Ms Nuland said Mr Bogdanov's comments demonstrated that Moscow now "sees the writing on the wall" on Syria and said Russia should now get behind efforts to prevent a wider bloodbath.
"They can withdraw any residual support for the Assad regime, whether it is material support [or] financial support," Ms Nuland said.
"They can also help us to identify people who might be willing inside of Syria to work on a transitional structure."
International envoy Lakhdar Brahimi, who has met Russian and US officials twice in the past week, is seeking a solution based on an agreement reached in Geneva in June that called for the creation of a transitional government in Syria.
But Russia has repeated warnings that international recognition of a new opposition coalition, notably by the United States, is undermining diplomacy, and rejected US contentions that the Geneva agreement sent a clear message that Mr Assad should must step down.
Ms Nuland said the Brahimi meetings could lay the framework for the political structure that follows Mr Assad.
"We've said all along to the Russians that we are concerned that the longer that this goes on, and the longer it takes us to get to an alternative political path for Syria, the only path is going to be the military one and that is just going to bring more violence, more destruction, more disruption and death inside Syria," Ms Nuland said.
"We all ought to be working together."