Food distribution in the southern Gaza city of Rafah has been suspended due to a lack of supplies and insecurity, the UN says.
The UN agency for Palestinian refugees, Unrwa, warned its distribution centre and a World Food Programme warehouse were now inaccessible because of the ongoing Israeli military action against Hamas in eastern Rafah.
An estimated 810,000 of the more than a million people taking refuge in Rafah have fled since the Israeli operation began on 6 May.
Unrwa also said its health centres had not received any medical supplies in the past 10 days.
The news came as the US said it did not believe any of the 569 tonnes of food and other aid that had entered Gaza through a newly-completed floating pier had been distributed to Palestinians by aid organisations.
On Saturday, crowds of Palestinians desperate for food intercepted several WFP lorries transporting aid from the pier to a warehouse in the central town in Deir al-Balah, which prompted the agency to suspend deliveries.
The WFP said distribution had been paused as the UN planned new routes to avoid crowds.
Meanwhile, the head of the World Health Organization warned that the largest partially functional hospital in northern Gaza was reportedly hit four times on Tuesday, as battles rage between Israeli forces and Palestinian armed groups in the nearby Jabalia area.
The Israeli military said it was reviewing reports from medics at Kamal Adwan hospital in Beit Lahia that its emergency department had been struck by Israeli missiles, forcing them to rush patients on hospital beds to a street outside.
The WHO also said al-Awda hospital in Jabalia had been besieged since Sunday, with dozens of staff, patients and people accompanying them trapped inside.