The UN has condemned the “large number of civilian casualties” caused by Israeli strikes on northern Gaza in recent days.

The comments – made by a spokesperson for Secretary General Antonio Guterres – come as at least 10 people have reportedly been killed by Israeli artillery fire at a food distribution centre at Jabalia refugee camp in northern Gaza, where Israeli tanks and troops are continuing a ground offensive.

The UN agency for Palestinian refugees (Unrwa) said shells hit inside and outside the centre on Monday morning as some hungry people were trying to get food handouts.

The Israeli military said it was reviewing the incident, adding that it operates “only against terror targets”.

Hundreds of people are reported to have been killed since the military said it was launching the offensive in the area and two neighbouring northern towns nine days ago to root out Hamas fighters who had regrouped there.

The UN said on Sunday that more than 50,000 people had fled the Jabalia area, but that others remained stranded in their homes amid increased bombardment and fighting on the ground. UN spokesperson Stephane Dujarric said civilians must “be protected at all times”.

“The secretary general condemns the large number of civilian casualties in the intensifying Israeli campaign in northern Gaza, including its schools, displacing sheltered Palestinian civilians,” he told reporters at a news conference in New York.

The offensive had also forced the closure of water wells, bakeries, medical points and shelters, as well as the suspension of other humanitarian services, including malnutrition treatment, it warned.

The UN said it had not been allowed to deliver essential supplies, including food, since 1 October, with two nearby border crossings closed and no deliveries allowed from the south.

The Israeli military said a convoy of 30 aid lorries entered through a crossing south of Gaza City on Sunday, when US President Joe Biden told Prime Minister Benjamin Netanyahu of what the White House called the “imperative to restore access to the north”.

The military has ordered residents of Jabalia and neighbouring areas to evacuate to the Israeli-designated “humanitarian area” in southern Gaza, saying it is “operating with great force against the terrorist organisations and will continue to do so for a long time”.

But many of the estimated 400,000 Palestinians living in the north say they are reluctant to flee to the south, fearing that if they do they will not be allowed to return home.

They believe the Israeli military is planning to implement a plan, proposed by retired Israeli generals, to completely empty the north of civilians and besiege Hamas fighters remaining there until they release Israeli hostages held since Hamas’s 7 October 2023 attack on Israel.

The Israeli military has denied it is implementing the plan. “We are making sure we’re getting civilians out of harm’s way while we operate against those terror cells in Jabalia,” spokesman Lt Col Nadav Shoshani told reporters.

Overnight, four people were killed when an Israeli aircraft struck a tented camp for displaced people next to al-Aqsa Martyrs hospital in the central town of Deir al-Balah.

The Israeli military said it had conducted a “a precise strike on terrorists who were operating inside a command-and-control centre in the area of a parking lot”, and that it took measures to mitigate harm to civilians.

“Shortly after the strike, a fire ignited in the hospital’s parking lot, most likely due to secondary explosions. The incident is under review,” Lt Col Shoshani wrote on X. “The hospital and its functionality were not affected from the strike.”

A video posted online appeared to show secondary explosions, but it was not clear whether they were caused by weapons or fuel tanks.

A spokesman for al-Aqsa hospital, Dr Khalil al-Daqran, said more than 50 tents were burned and that it was struggling to treat about 50 people who were injured, including children, women and the elderly, as well as casualties from other recent Israeli strikes.

A resident of the camp, Umm Mahmoud Wadi, said her family lost everything.

“Where should I take my daughters? Winter is coming. There’s no bedding, no clothes, nothing. I’m devastated. The gas bottle exploded – and we [our world] exploded.”

On Sunday night, more than 20 people were reportedly killed by tank fire at a UN-run school being used as a shelter for displaced families in Nuseirat refugee camp, which just north of Deir al-Balah.

A spokeswoman for Unrwa told the BBC that it had been “another night of absolute horror for people in the Gaza Strip”.

Louise Wateridge said the severe damage to al-Mufti school in Nuseirat meant it could not be used for the second round of the major polio vaccination campaign in Gaza, which began in the centre of the territory on Monday.

Local medics and Unrwa workers are leading the effort to give drops of the vaccine to 590,000 children aged under 10 over the next two weeks.

The campaign was organised by the World Health Organization (WHO) and Unicef after the first case of polio in two decades was discovered in an unvaccinated baby in central Gaza, where 80% of Gaza’s 2.3 million population is now sheltering.

UN officials are pressing for humanitarian pauses to be respected during the vaccination drive.

“This is critical because we cannot issue vaccinations for children who are fleeing for their lives, who are forcibly displaced. We cannot issue vaccination while there are bombs coming from the sky,” Ms Wateridge said.

She added: “These pauses are in the daytime, there are very specific timeframes for us to reach these thousands of children. The strikes and the military operations do continue around that and it’s incredibly dangerous and terrifying experience to run any kind of humanitarian response in these conditions.”

Israel launched a campaign to destroy Hamas in response to the group’s unprecedented attack on southern Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.

More than 42,280 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.