“This is the highest number of deaths among our personnel in a single incident,” UNRWA said in a post on social media platform X, formerly Twitter.
At least 34 people were killed in the attacks, according to media reports.
UNRWA said the shelter manager and other staff members were among the victims.
Guterres: Killings are “totally unacceptable”
UN Secretary-General António Guterres deplored the bloodshed.
“What is happening in Gaza is totally unacceptable,” he wrote in X.
“These dramatic violations of international humanitarian law must end now.”
It is not a goal
The UNRWA school in Nuseirat, located in the central Gaza Strip, was home to some 12,000 displaced people, mainly women and children.
This was the fifth attack since the conflict began 11 months ago.
Earlier on Wednesday, the UN said the site had previously been disassociated from Israeli forces.
UNRWA urged all parties to the conflict never to use schools or the areas surrounding them for military or combat purposes.
“No one is safe in Gaza. No one is spared. Schools and other civilian infrastructure must be protected at all times, they are not a target,” the tweet read.
'Endless and senseless killings'
UNRWA Commissioner-General Philippe Lazzarini deplored the “endless and senseless killings, day after day” in Gaza.
Writing in X, he said at least 220 agency employees have lost their lives since the war began.
“Since the beginning of the war, there has been a flagrant and relentless disregard for humanitarian personnel, facilities and operations,” he said, warning that “the longer impunity prevails, the more irrelevant international humanitarian law and the Geneva Conventions will become.”
Om Samir, a mother from Gaza City, with her children at an UNRWA school where the polio vaccination campaign is taking place.
The campaign against polio continues
Meanwhile, the UN said health workers were continuing their efforts to vaccinate young children in northern Gaza against polio, part of a broader campaign to defeat the disease, which can cause paralysis.
More than 81,600 children have been vaccinated as of Tuesday, according to preliminary data from the World Health Organization (WHO).
Polio was detected in Gaza in June and this month UN agencies and partners launched a two-round campaign to provide more than 640,000 children with two doses of the new oral polio vaccine type 2.
So far, nearly 528,000 children have been reached in the first round.
“More than 230 teams are on the ground trying to reach all children under 10 with the first batch of polio vaccine,” UN spokesman Stéphane Dujarric said in New York, adding that “they will have to do this again in four weeks.”
The health system in ruins
The campaign is taking place while Gaza's health system remains in dire condition.
The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) and its partners said half of all essential medicines are unavailable in the enclave, while primary health centres face critically low levels of insulin.
In addition, routine vaccinations to protect babies against tuberculosis, diphtheria, tetanus and whooping cough are also nearly exhausted.
Military operation in the West Bank
The United Nations and its partners also continue to support Palestinian civilians in the West Bank who have been affected by the 10-day Israeli security operation in Jenin and Tulkarm, as well as in the adjacent refugee camps.
This includes the delivery of food and water, and OCHA is coordinating efforts to provide additional assistance.
Over the weekend, the Office, together with UNRWA and other humanitarian partners, began assessing the needs of Palestinians affected by the operation.
Damage and displacement
More than 620 people, more than a third of them children, remain displaced and some 2,400 housing units have been damaged and more than 100 have been rendered uninhabitable.
During the operation, more than 2.6 kilometres of water and sewage networks in the Tulkarm and Nur Shams refugee camps were destroyed, severely hampering the provision of essential services.
As a result, more than 33,000 residents have had to deal with water outages and sewage flooding over the past two weeks.
