A Palestinian girl inside her family s partially destroyed home, looks at the destruction outside, in the Shejaiya neighbourhood of Gaza City. UNICEF
Volker Turk said that in such "apocalyptic" humanitarian circumstances, there was a high risk of atrocity crimes being committed.
"Civilians in Gaza continue to be relentlessly bombarded by Israel and collectively punished, suffering death, siege, destruction and deprivation of the most essential human needs such as food, water, lifesaving medical supplies and other essentials on a massive scale," he told a press conference.
"Palestinians in Gaza are living in utter, deepening horror."
He said 1.9 million of the 2.2 million people living in the Palestinian enclave had been displaced and were being pushed into "ever-diminishing and extremely overcrowded places in southern Gaza, in unsanitary and unhealthy conditions".
"The catastrophic situation we see unfolding in the Gaza Strip was entirely foreseeable and preventable. My humanitarian colleagues have described the situation as apocalyptic.
"In these circumstances, there is a heightened risk of atrocity crimes," the United Nations high commissioner for human rights said.
"As an immediate step, I call for an urgent cessation of hostilities and the release of all captives."
Turk said the human rights crisis in the occupied West Bank was also "extremely alarming", as he called for the Israeli authorities to take immediate steps to end "widespread impunity" for violations.
The latest toll from the Gaza media office said at least 16,248 people in Gaza, including more than 7,000 children and nearly 5,000 women, had been killed.
"All parties are aware of what is really needed to achieve peace and security for Palestinian and Israeli peoples; violence and vengeances can only result in more hatred and radicalisation," Turk concluded.
"The only way to end the accumulative sufferings is ending the occupation and achieving the two-state solution."
* This story was edited by Ahram Online.