The Tartus naval base and Hmeimim air base are Russia's only military outposts outside the former Soviet Union and have been key to the Kremlin's activities in Africa and the Middle East.

The ousting of Moscow's long-time ally Assad in a shock rebel offensive has brought their future into question.

"There are no final decisions on this," Kremlin spokesman Dmitry Peskov told reporters on Monday.

"We are in contact with representatives of the forces that now control the situation in the country," he added.

Russia said Sunday it had evacuated some of its diplomatic staff from the country.