Israel continued to pound the Gaza Strip on Sunday in an escalating air and ground campaign as the U.N. warned civil order was "starting to break down" in the besieged Palestinian territory.

Despite calls for a humanitarian ceasefire and outrage across the Muslim world, Israel has intensified its indiscriminate attack on Gaza, in response to the Oct. 7 Hamas incursion.

The Hamas-run health ministry in Gaza says the unrelenting retaliatory Israeli bombardment has killed more than 8,000 people, mainly civilians and half of them children.

Israel's army said "stage two" of the war started with ground incursions since late Friday.

On Sunday the military said it had struck another 450 Hamas targets within the past 24 hours, and that it was increasing its ground forces in Gaza.

'Nightmare'

Panic and fear have surged inside Gaza, where more than half of its 2.4 million residents are displaced, according to the U.N., and thousands of buildings have been destroyed.

U.N. chief Antonio Guterres said the situation was "growing more desperate by the hour" as casualties increase and essential supplies of food, water, medicine and shelter dwindle.

He reiterated appeals for a ceasefire to end the "nightmare."

The U.N. agency for Palestinian refugees, UNRWA, on Sunday said "thousands of people" broke into several of its warehouses and distribution centers in Gaza, grabbing basic survival items like wheat flour and hygiene supplies.

"This is a worrying sign that civil order is starting to break down," it said.

Inside Gaza, where petrol and diesel have virtually run out, donkey cart driver Raafat Najjar told AFP "there are no cars, we transport (people) on carts as there's no fuel."

Communications went down for days after Israel cut internet lines, although connectivity was gradually returning on Sunday.

Mirjana Spoljaric, president of the International Committee of the Red Cross, voiced shock at the "intolerable level of human suffering" in Gaza and urged all sides to de-escalate.

"This is a catastrophic failing that the world must not tolerate," she said.

'All areas are dangerous'

Defense Minister Yoav Gallant has said Israel was attacking "above the ground and below," alluding to Hamas's sprawling tunnel network.

Israeli fighter jets again dropped leaflets over Gaza City on Saturday, warning residents that the northern area was now a "battlefield" and they should "evacuate immediately."

Hamas authorities reported Sunday that a "large number" of people were killed overnight in strikes on two refugee camps in northern Gaza.

Israeli military spokesman Daniel Hagari reiterated that Palestinian civilians should go south "to a safer area where they can receive water, food and medicine."

After 84 aid trucks entered the territory in recent days, he vowed humanitarian efforts to Gaza would expand.

But Ibrahim Shandoughli a 53-year-old from Jabaliya in northern Gaza, told AFP he and his family went nowhere.

"Where do you want us to evacuate to? All the areas are dangerous."