Hawzah News Agency - A military media unit said a suicide attacker had detonated a car bomb near the convoy.
Pictures posted on state media showed what appeared to be the aftermath of the explosion, with bodies lying on the ground and fires belching out thick black plumes of smoke. Buses were
blackened by the blast with their windows blown out.
The blast hit the Rashidin area on Aleppo's outskirts, where dozens of buses carrying mostly Shi'ite residents of two villages that are being evacuated in a deal between warring sides were waiting to
enter the city.
Syrian state TV said an unknown number of people had been killed and wounded.
The British-based Syrian Observatory for Human Rights reported casualties, saying the explosion appeared to be caused by a bomb.
The buses had been waiting since late on Friday outside the city while the evacuation deal halted.