Israeli authorities rejected 82 out of 91 requests made by the UN to deliver aid to northern Gaza between early October and 25 November, UNRWA said in an on Thursday.
Israel also obstructed nine other attempts to transport humanitarian supplies to the northern region, which has been under a military siege and relentless bombardment for 50 days.
"The conditions for survival are steadily worsening for the estimated 65,000-75,000 people still residing there," the UN agency for Palestinian refugees (UNRWA) stated on social media site X.
The agency added that Jabalia, Beit Lahia and Beit Sahour have been cut off from aid for weeks, essentially since Israel began its renewed assault and siege on the north of Gaza on 5 October.
The update from UNRWA also highlighted that weather conditions within the north of the Strip in recent days have only made things worse for the already precarious population.
"It has rained heavily the last 3 days and temperatures have dropped," the agency stated.
"Thousands of families who have fled the besieged areas are now sheltering in the cold and rain without blankets, mattresses or waterproof shelters. The situation is beyond miserable."
UNRWA’s update comes after UK NGO Oxfam on Wednesday that Israel was "in the late stages of the ethnic cleansing of the North Gaza governorate" by blocking aid, and that Palestinian children are "starving to death" as a consequence.
"Our staff in Gaza have been desperately trying for nearly two months to reach starving civilians but have been blocked by the Israeli military. We know that many children are trapped and will be starving to death," Oxfam Executive Director Amitabh Behar said in a statement.
Behar also said that Israel was operating with international "impunity" and that it is laying the ground for "long-term military infrastructure" in the north, which he described as a "de-facto annexation of the land".
"The international community remains impotent and, in some cases, fully complicit. This is a dark moment in history as Israel is subjecting thousands of men, women and children to starvation as a weapon of war while world leaders look on in full awareness and choose to do nothing," Behar said.
Around 50,000-70,000 Palestinian civilians remain trapped in northern Gaza, with Israel driving the rest out by means of military assault and siege.
On Thursday morning, at least six people were killed in two separate Israeli airstrikes on a house and near Kamal Adwan hospital in Beit Lahia in the north out of a total of at least 17 killed around the whole Strip.
Many aid organisations, rights groups and aid organisations accuse Israel of implementing the so-called "Generals' Plan", devised by retired Israeli army Major General Giora Eiland, which proposes ethnically cleansing northern Gaza's civilian population by the means of military assault and total siege in order to create a temporary or permanent buffer zone in north Gaza.