"I am deeply concerned about the clear violations of international humanitarian law that we are witnessing in Gaza. Let me be clear: No party to an armed conflict is above international humanitarian law," Guterres told a Security Council session, without explicitly naming Israel.

Guterres, who personally traveled to the crossing between Egypt and Gaza in a push to let in assistance, welcomed the crossing of three aid convoys so far through the Rafah crossing.

"But it is a drop of aid in an ocean of need. In addition, our UN fuel supplies in Gaza will run out in a matter of days. That would be another disaster," Guterres said.

"To ease epic suffering, make the delivery of aid easier and safer, and facilitate the release of captives, I reiterate my appeal for an immediate humanitarian ceasefire."

The Security Council session is bringing together top diplomats including Secretary of State Antony Blinken, who has previously rejected calls for a ceasefire, saying it would only allow Hamas to regroup.

Hamas militants who stormed into Israel from the Gaza Strip on October 7 killed at least 1,400 people and took more than 220 captives, according to Israeli officials.

More than 5,700 Palestinians have been killed across the Gaza Strip in retaliatory Israeli bombardments, the Palestinian health ministry said.