UN human rights experts on Friday condemned in the "strongest possible terms" any attempts to "delegitimise" the Palestinian refugee agency UNRWA.
Several countries suspended their funding to the organisation last week, in response to Israeli allegations that a dozen staff members were involved in the 7 October attacks on southern Israel.
"The grossly disproportionate decision to suspend funding by some of the largest donor states defies the basic principle of humanity, and goes against states’ commitment to leave no one behind," the UN experts said in a .
"Denying basic human necessities, life-saving medical care, food, shelter, and antenatal care for pregnant women, is not just indefensible – it is a hindrance to the already complex journey toward peace," they added.
Among the 18 states that suspended funding to UNRWA are key donors including the US, Germany and UK.
The agency employs over 13,000 people in Gaza alone and provides vital services to the Palestinian territory's population.
UN special rapporteur Francesca Albanese warned last week that the suspension of aid based on the alleged actions of a handful of employees could be considered collective punishment and a violation of the Genocide Convention.
"These (funding cut) announcements come at an existential moment for over two million Palestinians in Gaza enduring catastrophic living conditions due to Israel’s large-scale military attack that the International Court of Justice (ICJ) considers a plausible genocide," the experts said, referring to an interim ruling by the world court last month.
Israel’s allegations against UNRWA staff came on the same day as the ICJ ordered Tel Aviv take measures to prevent genocidal acts and ensure humanitarian aid can enter the besieged Palestinian enclave.
The decision by the 18 states to defund UNRWA flies in the face of the ICJ ruling, with the agency's work almost impossible to replicate by any other aid organisation.
UNRWA itself has warned that its operations in Gaza could collapse by February.
"If the funding remains suspended, we will most likely be forced to shut down our operations by end of February not only in Gaza but also across the region," agency head Philippe Lazzarini said in a statement on Thursday.
On the same day as the 7 October attacks, Israel launched a brutal onslaught on Gaza that has so far killed more than 27,000 people and displaced almost all of the Palestinian territory's 2.3 million inhabitants.
Among those killed in Gaza since 7 October are more than 150 UNRWA staff.