The UN rights chief said the "darkest moment" of the conflict in Gaza was unfolding in the north of the territory, warning Friday that Israel's actions could amount to "atrocity crimes".
Volker Turk pointed out that already "more than 150,000 people are reportedly dead, wounded or missing in Gaza" since the war there erupted just over a year ago.
"Unimaginably, the situation is getting worse by the day," he said.
"My gravest fear is, given the intensity, breadth, scale and blatant nature of the Israeli operation currently underway in North Gaza, that number will rise dramatically."
Turk, the United Nations High Commissioner for Human Rights, warned that Israel's policies in northern Gaza "risk emptying the area of all Palestinians".
"We are facing what could amount to atrocity crimes, including potentially extending to crimes against humanity."
He called on the world's leaders to act, stressing that all states are obligated under the Geneva Conventions to ensure respect for international humanitarian law.
His statement stressed the urgency of the situation, warning that "today the darkest moment of the Gaza conflict is unfolding in the north of the Strip, where the Israeli military is effectively subjecting an entire population to bombing, siege and risk of starvation".
"The bombing in North Gaza is non-stop," he said.
At the same time, "the Israeli military has ordered hundreds of thousands to move, with no guarantees of return. But there is no safe way to leave," he warned.
The UN rights chief cautioned that there was "extremely limited access to this part of Gaza, (and) next to no aid has reached the area in weeks, with unlawful restrictions remaining".
"Many are now facing starvation."
At the same time, he said, "the Israeli military is striking hospitals, and staff and patients have been killed and injured or forced to evacuate simultaneously".
Turk's statement pointed out that Palestinian armed groups also reportedly continue to operate among civilians, including in places of shelter, putting civilians in harm's way "which is totally unacceptable".