The origin of the blast was not immediately clear and could have been caused by an air strike or an incident at an ammunition depot, said the Syrian Observatory for Human Rights.
"A powerful explosion went off late yesterday in an area of southern Aleppo province," the Britain-based monitoring group said.
The war monitor's head, Rami Abdel Rahman, said the area was known to host Iranian forces deployed in Syria to support President Bashar al-Assad's regime as well as allied Afghan fighters from the Fatemiyoun Brigade.
Western powers carried out their biggest attack on Assad's regime before dawn yesterday with strikes on targets they said were linked to Syria's chemical weapons programme.
Israel, which was not involved in yesterday's unprecedented wave of missile strikes but expressed full support, has unilaterally launched air raids on targets inside Syria on several occasions.
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