Gaza City, Gaza - Desperate Palestinians in Gaza burst into aid centers after more than three weeks of siege and bombardment, the UN said on Sunday, as Israel escalated ground operations.

Despite calls for a humanitarian ceasefire, international outrage, and the potential risk to hostages held in Gaza, Israel has intensified the war triggered by Hamas's unprecedented October 7 attack that killed 1,400 people.

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

Panic and fear have surged inside the Palestinian territory, where the UN says more than half of its 2.4 million residents are displaced and thousands of buildings destroyed.

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

The UN agency for Palestinian refugees, UNRWA, 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.

Communications were 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 suffering in Gaza and urged all sides to de-escalate.

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

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The Palestinian Red Crescent, meanwhile, said it had been ordered by Israel to evacuate the al-Quds hospital, where as many as 14,000 people are sheltering, according to the organization.

"We have over 400 patients who are inside the hospital, many of them are in the intensive care unit. Evacuating them means killing them. That’s why we refuse the evacuation order," a spokesperson said, per the Guardian.

With alarm growing, US National Security Advisor Jake Sullivan told CNN that the "burden" lies with Israel to distinguish between Hamas militants and innocent civilians in Gaza, with President Joe Biden reiterating the position in a call with Israeli Prime Minister Benjamin Netanyahu.

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

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."

However, Israel has repeatedly bombed the south of the strip as well, with many Palestinians pointing out no part of the territory is safe at the moment.

"Where do you want us to evacuate to? All the areas are dangerous," Ibrahim Shandoughli, a 53-year-old from Jabaliya in northern Gaza, told AFP.

The families whose loved ones were abducted by Hamas are also increasingly furious with their government's response.

"We demanded that no action be taken that endangers the fate of our family members," said Meirav Leshem Gonen, the mother of hostage Romi Gonen.

Hamas's armed wing, the Ezzedine al-Qassam Brigades, said it was prepared to release the hostages if Israel freed the thousands of Palestinian prisoners it was holding.

Ifat Kalderon, whose cousin Ofer Kalderon is believed held in Gaza along with other relatives, told AFP she supported the idea of a prisoner release in exchange for the hostages.

"Take them, we don't need them here," she said, referring to Palestinian detainees. "I want my family and all the hostages to come back home."