BEIRUT (AP) — A medical relief organization says four of its staff have been killed in an attack on a medical facility in Syria.

The International Union of Medical Care and Relief Organizations says an airstrike Tuesday night in northern Syria leveled a medical triage point in rebel-held territory outside the contested city of Aleppo.

The Britain-based Syrian Observatory for Human Rights monitoring group puts the toll at 13 dead, among them four nurses and paramedics and nine rebel fighters, some of them belonging to the al-Qaida-linked Fatah al-Sham Front.

It says the triage point was located in the rebel-held town of Khan Touman, south of Aleppo.

There were no reports on who was behind the strike.