There is only enough fuel to run health services in the south of Gaza for three more days, the World Health Organization said on Wednesday.
Hundreds of thousands of Palestinians have sought refuge in the south of Gaza from combat further north in the enclave. Israel has threatened a major assault on the southern city of Rafah to defeat thousands of Hamas terrorists it says are holed up there, and its troops are now battling Hamas on Rafah's outskirts.
The WHO said a delivery of fuel to the area had been denied on Wednesday.
"WHO has pre-positioned some supplies in warehouses and hospitals, but without more aid flowing into Gaza, we cannot sustain our life-saving support to hospitals," said WHO chief Tedros Adhanom Ghebreyesus, adding that WHO would remain in the area to provide health services.