President Vladimir Putin announced out of the blue on Monday that "the main part" of Russian armed forces in Syria would start to withdraw, telling his diplomats to step up the push for peace as U.N.-mediated talks resumed on ending the five-year-old war.
Damascus rejected any suggestion of a rift with Moscow, saying President Bashar al-Assad had agreed on the "reduction" of Russian forces in a telephone call with Putin.
Western diplomats speculated that Putin may be trying to press Assad into accepting a political settlement to the war, which has killed 250,000 people, although U.S. officials saw no sign yet of Russian forces preparing to pull out.
The anti-Assad opposition expressed bafflement, with a spokesman saying, "Nobody knows what is in Putin's mind".
Russia's military intervention in Syria in September helped to turn the tide of war in Assad's favour after months of gains in western Syria by rebel fighters, who were aided by foreign military supplies including U.S.-made anti-tank missiles.
Putin made his surprise announcement, that came with no advance word to the United States, at a meeting with his defence and foreign ministers.
Russian forces had largely fulfilled their objectives in Syria, Putin said. But he gave no deadline for the completion of the withdrawal and said forces would remain at a seaport and airbase in Syria's Latakia province.