A deadly suicide bombing during Sunday mass at Mar Elias Church, just outside Damascus, left at least 20 people dead and 52 others injured, marking one of Syria’s worst attacks on a place of worship in recent years.

The attacker opened fire before detonating his explosives. It was the first such church attack in Syria in years. The Interior Ministry blamed ISIS, though no group has claimed responsibility.

Witnesses reported chaos, a second possible gunman, and scenes of devastation. Officials condemned the act and pledged to fight extremism.