The immediate aftermath of the Aleppo bus convoy blast
The British-based Syrian Observatory for Human Rights reported casualties, saying the explosion appeared to be caused by a bomb.
Syrian state TV said an unknown number of people had been killed and wounded.
The blast hit the Rashidin area on the outskirts of the war-ravaged city where dozens of buses were lined up.
Thick black smoke rises from the Aleppo bus convoy blast scene
The buses were carrying mostly Shi'ite residents of two villages being evacuated as part of a deal between warring sides.
They had been waiting since late on Friday outside the city while the evacuation deal halted.
Terrified women and children seek shelter after the Aleppo bus convoy blast
Several people were killed or injured in the blast
A military media unit run by Damascus ally Hezbollah 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.
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The buses were blackened by the blast with their windows blown out.