Two Palestinians have been killed in an explosion in the northern Gaza Strip, Palestinian medics and local witnesses say. 

The Popular Resistance Committees group said that the explosion in Beit Hanoun on Saturday had been caused by an Israeli air raid, but a military spokesman denied any attack had been carried out.

"We haven't carried out a strike in northern Gaza in recent hours. The explosion might be due to mishandling of weapons," the Israeli army spokesman said.

At least one of the dead was reported to have been preparing to fire a rocket when the blast occured.

The incident came as Mahmoud Abbas, the Palestinian president, and Ehud Olmert, the Israeli prime minister, agreed to meet to discuss the faltering truce between Israeli forces and Hamas in the Gaza Strip.

Fighters in the Gaza Strip, which has been fully controlled by Hamas since security forces loyal to Abbas were pushed out in June 2006, have launched a number of rocket and missile attacks on southern Israel over the last 12 days.

Israel has responded by launching air raids and keeping border crossings into the territory closed to deliveries.

UN aid stopped

UN aid workers turned away thousands of Gaza residents from distribution centres on Saturday after supplies of rice, flour, sugar and oil ran out

About 750,000 Palestinians in Gaza are eligible for food aid.

"All Palestinians depend on foreign aid because all the crossings are closed, there is no work, no jobs, there is nothing," Myassar Abu Alaban, a Gaza resident, said.

"If aid is cut off to the people what can they do? Especially those with large families? This danger threatens three-quarters of the Palestinian population."

Israel and Hamas blamed each other for the recent flare-up in the fighting which is threatening to end a five-month old truce between the two sides.

"Hamas is directly responsible for the escalation in the violence," Mark Regev, an Israeli government spokesman, said.

"Israel had wanted to see the calm that prevailed until recently prevail once again. But Hamas ... are seeking a dangerous escalation."

But Mahmoud al-Zahar, a senior Hamas leader, said "self-defence and resistance" would continue and told Israel that if they wanted to continue the truce, "then abide by it".

"Up to this moment we are committed to the ceasefire," he said.

"But if the Israelis decide to go away from the ceasefire we are ready ... We are waiting for the Israelis. If they are committed really we have to address that frankly."