"Given the high number of civilian casualties & the scale of destruction following Israeli airstrikes on Jabalia refugee camp, we have serious concerns that these are disproportionate attacks that could amount to war crimes," the office wrote on X.

Israel struck Jabalia for the second time within two days on Wednesday. The Israeli military said the strikes that hit the densely populated camp killed Muhammad A'sar, the head of Hamas' anti-tank missile unit, but the Israeli claim is not confirmed.

Gaza's Health Ministry said scores of people were killed and wounded in the Wednesday airstrikes, but the death toll is not clear. A day earlier, Israeli warplanes hammered Jabalia, killing at least 50 people.

After the Tuesday attack, an Israeli military spokesman acknowledged that Jabalia was full of innocent civilians, including women and children. "This is the tragedy of war … we've been saying for days, move south," the spokesman said.

UN humanitarian chief Martin Griffiths also condemned the Israeli strikes on Jabalia. "This is just the latest atrocity to befall the people of Gaza where the fighting has entered an even more terrifying phase, with increasingly dreadful humanitarian consequences," he said.