The Syrian Observatory for Human Rights had earlier stated that the air strike took place on Monday at dawn, hitting a building in the town of Al Mayadin that was being used as a prison.
London-based war monitor says air strikes again targeted Syria's rebel-held province of Idlib on Saturday.
An alleged chemical attack that killed at least 58 and injured dozens in the rebel-held town of Khan Shaykhun in Idlib province has triggered global criticism.
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