Russia and China have resisted diplomatic efforts to join the U.S. and other Western governments in calling for Assad's resignation, and have blocked a United Nation's Security Council resolution condemning the government crackdown that has led to the deaths of thousands of Syrians.
But on Monday Mikhail Margelov, a special envoy of President Dmitry Medvedev, said Russia's diplomatic efforts to resolve the conflict have been exhausted.
"[Our] veto on the U.N. Security Council resolution was the last instrument allowing Bashar al-Assad to maintain the status quo in the international arena," Margelov said, according to the state-run Itar-Tass news agency.
Moscow has opposed sanctions, but has made public statements urging Assad to implement a series of reforms. Russia introduced a draft of a Security Council resolution last year. But the U.S. and its allies have accused Russia of using that resolution and other ploys to buy time for Damascus.