6 UNRWA staff killed in Israeli attack on UN-run school in Gaza: Guterres

"What's happening in Gaza is totally unacceptable. A school turned shelter for around 12,000 people was hit by Israeli airstrikes again today,” Antonio Guterres said on X.

"Six of our @UNRWA colleagues are among those killed," he added.

His remarks came after at least 18 people were killed Wednesday in an Israeli bombing of al-Jaouni School housing displaced civilians in central Gaza, with several injured.

"These dramatic violations of international humanitarian law need to stop now," Guterres said.

UNRWA said this was "the highest death toll" among its staff in a single incident.

"Among those killed was the manager of the UNRWA shelter and other team members providing assistance to displaced people. Sincere condolences to their families and loved ones," it said on X.

The school has been hit five times since the Gaza war began last October, it said, adding: "Schools and other civilian infrastructure must be protected at all times. They are not a target."

Israel has continued its brutal offensive on Gaza since a cross-border attack by the Palestinian group Hamas early last October, despite a UN Security Council resolution demanding an immediate cease-fire.

Nearly 41,100 people, mostly women and children, have since been killed and more than 95,000 injured, according to local health authorities.

The Israeli onslaught has displaced almost the entire population of the territory amid an ongoing blockade that has led to severe shortages of food, clean water and medicine.

Israel faces accusations of genocide for its actions in Gaza at the International Court of Justice (ICJ).