Israel has claimed responsibility for an attack on an ambulance outside Gaza City’s Al-Shifa Hospital, the largest medical facility in the enclave, which witnesses say killed and wounded dozens of people.

At least 15 people were killed and 50 others wounded, the Hamas-run health authorities said Friday. Footage from the scene showed at least a dozen bloodied casualties strewn across the ground near an ambulance. There appears to be some shrapnel damage to at least one of the cars on the scene.

Israel said it had targeted the ambulance because it was being used by Hamas, according to a statement from the Israel Defense Forces (IDF). “An IDF aircraft struck an ambulance that was identified by forces as being used by a Hamas terrorist cell in close proximity to their position in the battle zone,” it wrote.

“A number of Hamas terrorist operatives were killed in the strike… We have information which demonstrates that Hamas’ method of operation is to transfer terror operatives and weapons in ambulances,” the statement said.

The ambulance strike prompted UN Secretary-General Antonio Guterres to reiterate his calls for a cessation of fire on Gaza, something Israel has rejected.

“I am horrified by the reported attack in Gaza on an ambulance convoy outside Al Shifa hospital,” Guterres said in a statement.

“The images of bodies strewn on the street outside the hospital are harrowing,” he said, adding: “I do not forget the terror attacks committed in Israel by Hamas and the killing, maiming and abductions, including of women and children. All hostages held in Gaza must be released immediately and unconditionally.”

“Now, for nearly one month, civilians in Gaza, including children and women, have been besieged, denied aid, killed, and bombed out of their homes,” he said, “This must stop.”

A spokesperson for the Palestinian Ministry of Health in Gaza, who was at Al-Shifa Hospital, said that Israel was responsible for the attack.

The Palestine Red Crescent Society (PRCS) said one of its ambulances was in the convoy but that none of its team members were injured in the strike.

The ambulance was damaged when a shell fell near it, the PCRS said. “Upon arrival at Al-Shifa hospital’s gate, the gate was targeted again,” PRCS said, adding that a separate Ministry of Health ambulance was then directly hit and dozens of civilians in the area were killed and injured.