Russia has for the first time conceded Syrian opposition forces could overthrow the government of President Bashar al-Assad.
Moscow's envoy to the Middle East, deputy foreign minister Mikhail Bogdanov, said rebels are gaining ground and victory by opposition forces cannot be ruled out.
He said President Bashar al-Assad's forces were losing more and more control and territory.
Russia, one of Syria's staunchest allies, was making plans for a possible evacuation of thousands of its citizens, he said.
The BBC reports that Mr Bogdanov's comments do not mean Moscow has changed its official position.
Russia still maintains that the ousting of President Assad would deepen the conflict, but this is the first time Russia has publicly acknowledged that the Syrian president faces possible defeat.
Mr Bogdanov repeated Russia's call for dialogue between the two sides, predicting that the fighting would grow more intense.
He said tens, possibly hundreds of thousands of people would be killed if that happened.
Russia, along with China, has used its veto at the UN Security Council to block resolutions condemning the Syrian government's use of violence.
Mr Bogdanov also raised concerns about "extremists" seizing chemical weapons arsenals, according to the Interfax news agency.
NATO Secretary General Anders Fogh Rasmussen earlier said the collapse of the Syrian government was only a question of time, adding that President Assad should initiate a process to accommodate the legitimate aspirations of the Syrian people.
