An explosion rocked an area in northern Syria near a base where pro-regime fighters and allied have been stationed.
A monitor said the origin of the blast was not clear and could have been caused by an air strike or an incident at an ammunition depot.
The war monitor’s head, said the area was known to host fighters to support President Bashar Al-Assad’s regime.
Western powers carried out their biggest attack on Assad’s regime before dawn on Saturday with strikes on targets they said were linked to Syria’s chemical weapons programme.
The pentagon subsequently said no further strikes were planned as part of an operation launched a week after a suspected chemical attack on the holdout rebel town of Douma killed dozens of people.