Bomb blasts in the Syrian cities of Homs and Damascus have left at least 140 people dead, monitors and state media say.

Double car bomb attacks kill at least 46 people in Syria's central city of Homs on Sunday as international efforts to bring about a ceasefire in the war-torn country have floundered.

Syrian rebels begin evacuating the last area they hold in the city of Homs under a ceasefire deal reached with the government, a monitoring group has said.

Russia appears to have begun carrying out air strikes in Syria against opponents of President Bashar al-Assad, a US defence official says.