The position of embattled Syrian President Bashar al-Assad became more precarious Monday after a top Kremlin aide said Russia was withdrawing its support from his administration. 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.