Several buses sent to transport the sick and injured from two government-held villages in Syria’s Idlib province have been burned by rebels.
It has thrown the latest efforts to evacuate besieged areas into doubt.
Pro-government forces say people must be allowed to leave the mainly Shia villages of Foah and Kefraya for the evacuation of east Aleppo to restart.
State media said convoys had begun to leave Aleppo on Sunday but other reports said they had turned back.
The initial plan to evacuate the last rebel-held enclaves in the city collapsed on Friday, leaving civilians stranded at various points along the route out without access to food or shelter.