Victory for the Syrian opposition could 'not be ruled out', Mr Bogdanov said
A Russian official has said for the first time that the Syrian government may be defeated by opposition forces.
President Bashar al-Assad's forces are "losing more and more control and territory", deputy foreign minister Mikhail Bogdanov said on Thursday.
Russia was also making plans for a possible evacuation of thousands of its citizens in Syria, Mr Bogdanov said.
Russia has been one of the staunchest international allies of Mr Assad's government.
"Unfortunately, we cannot rule out the victory of the Syrian opposition," Mr Bogdanov said.
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.
"If such a price for ousting the president seems acceptable to you, then what can we do? We consider it unacceptable," he said.
Mr Bogdanov also raised concerns about "extremists" seizing chemical weapons arsenals, according to the Interfax news agency.
Western nations have in recent days raised the prospect of Syrian government forces themselves using chemical weapons.
Mr Bogdanov's comments do not mean Moscow has changed its official position, the BBC's Steve Rosenberg in Moscow reports.
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, our correspondent adds.
In Syria itself, state media reported a blast in the Damascus suburb of Qatana which it said killed 16 people, including seven children.