The UN Secretary General has said the UN Palestinian refugee agency (UNRWA) is "the backbone of all humanitarian response in Gaza".
Antonio Guterres was speaking in the wake of allegations that 12 UNRWA staff members took part in the Hamas attacks on 7 October last.
Major donors to the agency including the United States, the United Kingdom and the European Union announced suspension of funding, pending an investigation into the allegations.
The UN terminated the employment of nine of the staff members implicated. UN officials said that one of the employees was deceased and the identities of the remaining two were being confirmed.
Yesterday evening, Mr Guterres met donors behind closed doors at UN headquarters, to appeal for a continuation of funding.
But ahead of the meeting, the US envoy to the UN, Linda Thomas-Greenfield told reporters that they would be looking for "fundamental changes" to UNRWA before the US would resume funding.
UNRWA provides aid to around two million people in Gaza and the US is its largest individual donor, contributing $300-$400 million per year to support Palestinian refugees across the region.
At a Security Council meeting this morning to discuss the crisis in the Middle East, the UN's Under-Secretary-General for Humanitarian Affairs, Martin Griffiths, described UNRWA as the "beating heart" of the humanitarian operation in Gaza.
"I am appalled that some UNRWA employees were allegedly involved in the attack in Israel on 7 October," Mr Griffiths told the council.
"These allegations must be addressed. UNRWA has taken swift action, and an investigation is under way," he said.
"But UNRWA's lifesaving services to over three-quarters of Gaza's residents should not be jeopardised by the alleged actions of a few individuals," he said.
Yesterday the Security Council heard from the UN's newly appointed Senior Humanitarian and Reconstruction Coordinator for Gaza, Sigrid Kaag. Her job is to facilitate, coordinate and monitor aid consignments into Gaza.
Following her first closed-door briefing to the council, Ms Kaag told reporters "there is no way any organisation can replace or substitute the tremendous capacity and the fabric of UNRWA and its ability and knowledge".
Gaza is under siege by Israel and facing a major humanitarian crisis, with entire neighbourhoods destroyed by bombing.
Some 1.7 million of Gaza's 2.4 million inhabitants have fled their homes, according to the UN.
Tánaiste and Minister for Foreign Affairs Micheál Martin said over the weekend that Ireland has "no plans" to suspend funding, which he called "vital".
The heads of the World Health Organization, the UN rights office, UNICEF and the World Food Programme warned that defunding UNRWA risked a "catastrophic" humanitarian collapse in Gaza.
"Withdrawing funds from UNRWA is perilous and would result in the collapse of the humanitarian system in Gaza, with far-reaching humanitarian and human rights consequences in the occupied Palestinian territory and across the region," said the statement from heads of organisations that form the UN Inter-Agency Standing Committee.
The unprecedented Hamas attack resulted in about 1,140 deaths, mostly civilians, in southern Israel, according to official figures.
Militants also seized 250 hostages, of whom Israel says around 132 remain in Gaza, including the bodies of at least 28 people.
Israel responded with a relentless military offensive that has killed at least 26,751 people in Gaza, mostly women and children, according to the health ministry in the territory.
Israel says UNRWA 'fundamentally compromised'
Israel has vowed to stop UNRWA's work in Gaza after the war and doubled down when government spokesman Eylon Levy said the agency "has been fundamentally compromised".
He accused it of "hiring terrorists on a massive scale, letting its infrastructure be used for Hamas military activity and relying on Hamas for aid distribution in the Gaza Strip".
UN Gaza aid coordinator Sigrid Kaag said earlier "there is no way that any organisation can replace or substitute (the) tremendous capacity, the fabric of UNRWA - (their) ability and their knowledge of the population in Gaza".
The US said it "very much supported" UNRWA's work.
"There is no other humanitarian player in Gaza who can provide food and water and medicine at the scale that UNRWA does," said State Department spokesman Matthew Miller.
"We want to see that work continued, which is why it is so important that the United Nations take this matter seriously, that they investigate, that there is accountability for anyone who is found to have engaged in wrongdoing."
