A strike this weekend on a school run by the UN that was being used for shelter by thousands of displaced people in northern Gaza Strip killed at least 24 people, a UN official said on Sunday.

Palestinian officials had said on Saturday that many people were killed and injured in an Israeli attack on the Al-Fakhura school, which was being used as a shelter by adults and children, in the Jabalia area of northern Gaza.

Philippe Lazzarini, head of the UN agency that aids Palestinian refugees, gave the death toll on Sunday and said that there were nearly 7,000 displaced people sheltering in the school when the strike hit. He did not give a number for the wounded or suggest who was responsible.

The Israeli military said that it had received reports of an incident Saturday in the Jabalia area and that it was under review, adding that it was “committed to international law including taking feasible steps to minimize harm to civilians.”

Lazzarini said another school, where about 4,000 displaced people were sheltering at the time, in Gaza City, was “directly struck” on Friday, and ambulances “could not reach the school to provide help”. His agency, the UN Relief and Works Agency, said it believed that scores of people had been either killed or wounded, but did not have exact numbers.

UN Secretary-General António Guterres said hundreds of thousands of Palestinian civilians have sought shelter at UN facilities throughout Gaza. “I reaffirm that our premises are inviolable,” he said on Sunday.

At least 176 displaced people sheltering at schools run by UNRWA have been reported killed and nearly 800 wounded since the start of Israel’s bombing campaign.