BEIRUT (AP) — A Syrian paramedic group active in opposition-controlled areas says gunmen have stormed one of its offices in northwestern Syria killing seven of its members and stealing two vehicles and other equipment.

The Syrian Civil Defense group, more popularly known as the White Helmets, said in a statement that the attack happened Saturday in the town of Sarmin.

The Britain-based Syrian Observatory for Human Rights said the seven were killed after being shot in the head, adding that the killings were discovered when volunteers from Syrian Civil Defense arrived to start a shift and found the bodies of their colleagues.

No one claimed responsibility for the rare attack but it came amid tension in the area. Sarmin is in Idlib province, which witnessed clashes recently between rival insurgent groups.