UN aid agencies say they have begun to significantly reduce their operations in the Gaza Strip because they have almost exhausted their fuel reserves.
Small quantities of fuel retrieved from existing reserves are being used to maintain the water supply in the south, where hundreds of thousands of people are sheltering from Israeli strikes.
However, they will run out on Thursday.
The agencies say they have reduced their support for overwhelmed hospitals and bakeries feeding the displaced.
"What we are seeing in the Gaza Strip is unprecedented," Juliette Touma of the UN agency for Palestinian refugees, Unrwa, told the BBC.
"Two million people are being strangled. Gaza is being choked with very, very little assistance that is coming from outside."
Israel began its bombing campaign in Gaza, cut off electricity and most water, and stopped imports of food, fuel and other goods in retaliation for a cross-border attack by Hamas on 7 October, in which at least 1,400 people were killed and 224 taken hostage.
Gaza's Hamas-run health ministry says 7,000 people have been killed in the territory since then and that its health system is facing total collapse, with a third of hospitals not functioning and the rest only treating emergency cases.