The latest Israeli attacks in northern Gaza, reportedly killing or injuring dozens, are having "an appalling impact on civilians enduring suffering and starvation," a UN spokesman said on Monday.

"We condemn the deadly escalation of the Israeli military offensive, which we saw over the weekend across Gaza City," said Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres. "We reiterate our call for the protection of civilians and humanitarian personnel, and full respect for international law."

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said thousands of displaced people fled heavy strikes and bombardment across the city on heavily congested Al Rashid Road, the only route available to the south.

Commissioner-General Philippe Lazzarini of the UN Relief and Works Agency for Palestine Refugees in the Near East said on Sunday that in the previous four days, 10 of the agency's Gaza City buildings were hit, including seven schools and two clinics used as shelters for thousands of the displaced.

He warned that as air strikes in Gaza City and the broader northern Gaza intensify, exhausted and terrified civilians are displaced yet again.

The World Food Program said that forced displacement from Gaza City exhausts families' resources and disrupts their last lifelines. Without safe, sustained access, the risk of worsening hunger grows, especially for children.

The top United Nations expert on Palestinian rights, Francesca Albanese, said on Sunday that Israel was trying to make Gaza City unlivable in its assault on the enclave's largest urban area and was endangering the lives of Israeli hostages. 

The Permanent Mission of Israel to the UN rejected Albanese's comments. Israel says the offensive to take control of Gaza City is part of a plan to defeat Palestinian militant group Hamas for good and that it has warned civilians to head south to a designated humanitarian zone. 

However, the UN and numerous countries say its tactics amount to forced mass displacement and that conditions in the humanitarian zone are dire, with food in short supply.

The Gaza health authorities said that three more people died due to malnutrition and starvation over a span of 24 hours. "Overall, the ministry reports that 425 people across Gaza have died due to malnutrition and starvation, about a third of them children, since October 7, 2023," OCHA said.

The nearly two-year campaign has killed more than 64,000 people, according to local authorities.

(With input from agencies)