Israeli Defence Minister Ehud Barak has agreed to partially lift Israel’s suspension of fuel supplies to the only power plant in the Gaza Strip.
The facility shut on Monday a week after Israel stopped fuel in response to rocket attacks from Hamas.
Meanwhile, the UN relief agency in Gaza said it would have to suspend its operations in 48 hours unless vital supplies were allowed into Gaza.
But Israel has said only fuel will be allowed to pass across the border.
Christopher Gunness, spokesman for Unrwa, the UN agency in Gaza, said its warehouses were running out of wheat, meat, powdered milk and cooking oil.
It is shameful and unacceptable that the largest humanitarian actor in Gaza is being forced into yet another cycle of crisis management
He said food distributions to 750,000 would have stop unless supplies made it through, calling the Israeli blockade “physical and mental punishment” of the population.
“It is also shameful and unacceptable that the largest humanitarian actor in Gaza is being forced into yet another cycle of crisis management,” Mr Gunness said.
Israeli officials said Mr Barak had agreed to a limited resumption of fuel supplies to Gaza following an appeal by Middle East Quartet envoy Tony Blair.
Mr Blair, the former British prime minister, was in Jerusalem after attending a meeting of the Quartet in Egypt on Sunday, aimed at resolving the conflict in the Middle East.
Last week, Israeli tanks and troops entered the Gaza Strip for the first time since an Egyptian-mediated ceasefire began in June. Six Palestinian militants were killed.
Meanwhile Hamas militants fired a barrage of rockets into southern Israel, which landed without causing casualties.
Most of Gaza City was plunged into darkness on Monday night as the electricity plant shut down.
The facility depends on supplies of industrial fuel, mainly paid for by foreign donors like the European Union, but transported through Israel.
For nearly a week the Israeli government has not allowed any goods into Gaza through its crossings, including fuel and food.
Israel says the Hamas authorities in Gaza have orchestrated an artificial crisis for political reasons.
‘Real and serious’
But the United Nations has described the fuel shortages as “real and serious”.
We were told we would not be allowed in today
Israel’s closure of the crossings has also kept journalists from entering Gaza for five days, drawing protests from the Tel Aviv-based Foreign Press Association.
The Gaza City plant provides about a quarter of the Gaza Strip’s electricity and more than half the electricity used by the city itself.
Most of the rest of the supply to the territory of 1.5 million people comes directly via power lines from Israel.
Palestinian engineers had been implementing a system of rolling blackouts to different areas of Gaza City to prevent the lines from Israel becoming overloaded and cutting out.