The death of 15 medics and humanitarian workers in Gaza after shots were fired at their ambulances raises further concerns of “war crimes by the Israeli army,” the UN High Commissioner for Human Rights said, AFP reports.

“I am appalled by the recent killings of 15 medical personnel and humanitarian aid workers, which raise further concerns over the commission of war crimes by the Israeli military,” Volker Turk told the UN Security Council.

Turk called for an “independent, prompt and thorough investigation” into the March 23 incident that Israeli officials have claimed was an attack on “terrorists.”