Israel has permitted limited aid and fuel deliveries into the Gaza Strip, which it has closed to virtually all supplies for the past three weeks.

Gaza's only power plant, which is in urgent need of spare parts, is to restart at reduced capacity.

Shortages and power cuts in the territory have led the UN to describe conditions there as the "worst ever".

Israel says the tightening of the Gaza blockade is a legitimate response to rocket fire by Palestinian militants.

Sixty trucks of supplies were scheduled to pass through the Kerem Shalom and Karni crossings on Wednesday, an Israeli government spokesman said.

Deliveries of industrial diesel and the first cooking gas to enter the Strip in three weeks are also due.

But the UN relief agency said it faced a "hand-to-mouth" situation.

Before Wednesday, it had been permitted to bring 16 trucks into Gaza in three weeks, but needed 15 a day to cover the basics, deputy commissioner general Filippo Grandi told AFP news agency.

Deliveries to some 750,000 people who rely on its food parcels have been interrupted in recent weeks because of shortages.

The power plant had been closed because it was damaged by frequent shutdowns due to fuel shortages and Israel was not allowing the necessary spare parts through the crossings, Gaza energy authorities said on Tuesday.

But the EU office that funds the plant said temporary repairs had been carried out, and one of its four turbines would be restarted.

The plant serves about a third of Gaza's population - the rest of the Strip's power comes from Israel and Egypt.

'No crisis'

The deliveries came as the UN and other aid agencies launched an appeal for $462m for programmes in the West Bank and Gaza, where they said conditions had continued to deteriorate during 2008.

The Israeli blockade of Gaza had "driven unprecedented numbers of Palestinians into unemployment and poverty," a report by the agencies said.

Also on Wednesday, a Libyan official told AFP a ship carrying 3,000 tonnes of humanitarian aid had set off for Gaza.

It follows three boats of European and Palestinian activists which have sailed to the Strip in recent months.

Israel says there is no humanitarian crisis in Gaza, although the head of the UN relief agency Unrwa said last week that the Strip was facing the worst period the agency had ever seen there.

Israel has also prevented foreign journalists from entering the territory, citing security concerns.

The Foreign Press Association in Israel has petitioned the Supreme Court against the restrictions and heads of major world news organisations have written to Israel's Prime Minister Ehud Olmert calling for access to the Strip.

The blockade was tightened after the current wave of hostilities broke out on 4 November.

Israeli forces launched an incursion into Gaza to destroy what it says was a tunnel intended for use to abduct its soldiers, and militant groups in Gaza responded with rocket fire.

The fighting has put increasing pressure on a five-month-old truce between Israel and the militant group Hamas, which controls Gaza.