Recent supplies of fuel from Israel have been sporadic
The United Nations says it has had to halt food distribution in the Gaza Strip because it has run out of fuel.
Distributions to 15,000 refugees took place on Thursday, but were then halted. Officials said deliveries due on Saturday will also not take place.
Israeli sanctions imposed in an attempt to curtail rocket fired by Palestinian group Hamas have caused shortages.
Reports say no fuel was pumped from Israel to Gaza on Thursday. Israel says Hamas is preventing fuel distribution.
It says there are a million litres of fuel at a border terminal which Gaza fuel distributors, with the backing of Hamas, have refused to collect in protest at the Israeli restrictions.
But the UN says fuel distributors who agreed to collect fuel not earmarked for the UN to help with distributions to refugees were stopped by protesters from the farming and fishing sectors - who have also been hit by the shortages.
In a briefing to the Security Council, Assistant Secretary General Angela Kane said Gaza had suffered "heightened humanitarian distress" caused by closed border crossings with Israel and Egypt, the shortage of basic food and commodities, poor water supplies and sanitation.
More than 80% of Gaza's population rely on humanitarian assistance, with UN food aid going to about 1.1 million people. A high proportion of them are children.
But Ms Kane warned that such assistance was now at risk of suspension because of the restrictions on vehicle fuel deliveries, which were tightened by Israel earlier this month after Palestinian militants attacked the Nahal Oz fuel terminal, killing two Israelis.
There have been no deliveries of petrol by Israel since 18 March and no deliveries of ordinary diesel since 2 April, according to UN officials.
"In an effort to save fuel, Unrwa has prioritised food distribution, solid waste removal, and sewage projects," she told the Security Council on Wednesday.
UN food aid goes to about 1.1 million people in the Gaza Strip
"Unless petrol is allowed in, Unrwa will discontinue its food assistance to 650,000 refugees, as well as its garbage collection services, which benefit half a million Gazans," she added.
"Another 500,000 Gazans are already living in 12 municipalities without any solid waste management capacity - largely due to the lack of fuel."
Hospitals and clinics will also run out of fuel within a week, she warned.
Public transport has been severely curtailed by the shortage of vehicle fuel, meaning that children cannot get to school and adults to work. Some car owners have converted their engines to run on cooking oil.
The fuel shortages have been compounded since 7 April by a strike by Gaza's fuel distributors and petrol station owners, who have been refusing to pick up about one million litres that Israel has pumped into the Nahal Oz fuel terminal, saying the quantity is insufficient.
The boycott has not affected industrial diesel supplies to Gaza's main power station, which was within hours of shutting down on Wednesday morning until Israel agreed to allow delivery of one million litres - enough to generate electricity for three days.
A spokesman for the Israeli government, Mark Regev, told the BBC that it was Hamas, and not Israel, that was causing the fuel and humanitarian problems.
"You have a situation where the Hamas regime in Gaza is deliberately holding up supplies for its own political reasons, which are difficult to understand," he said.
"But the truth is there's a very consistent pattern here. The oil terminal itself was deliberately targeted by Hamas just a few days ago, that was the second attack in that vicinity in a very short period of time," he added.
"The terrorist regime in Gaza is deliberately attacking the crossings that supply the Gaza people with these important supplies."
On a visit to Gaza on Wednesday, the UN special envoy Robert Serry, condemned the militant attacks, but also described Israel's policies as "collective punishment".
At the UN Security Council meeting, Ms Kane also criticised Israel for failing to fully implement a recent pledge to remove 50 roadblocks in the occupied West Bank - only 44 of the roadblocks were removed, of which five were significant, she said.
She added that Israel continued to violate Lebanese airspace - sorties by Israeli aircraft over Lebanon increased from 282 in February to 692 in March and 476 in the first half of April alone, she said.
The Security Council session ended shortly after her statement, however, when Western representatives walked out in protest at comments made by the Libyan representative, Giadalla Ettalhi, who likened Gaza to a Nazi death camp.
"A number of Council members were dismayed by the approach taken by Libya and do not believe that such language helps advance the peace process," British official Karen Pierce said afterwards.