for the Middle East, blamed the conflict on "the irresponsibility of Hamas rocket attacks and the excessiveness of Israel's response".

He said a ceasefire was needed to halt the violence but added: "We must create new conditions on the ground to ensure this does not happen again."

Serry said the Palestinian Authority, now run by Fatah, would have to take control of the crossings in Gaza, even though the strip is under the control of Hamas and the factions are bitter rivals. Asked if there would in future be international peacekeepers or monitors in Gaza, he said: "We have to look into possibilities like an international presence."

Gaza's sole power plant has not worked since Monday because Israel has halted deliveries of industrial diesel. Hospitals are overwhelmed and there is not enough wheat grain for UN food deliveries, UN officials said.

A cash shortage in Gaza meant the UN could not continue cash assistance to 95,000 of the very poor. It could only meet half its December staff salary payments and was reduced to bartering with flour in some instances.

In Israel, the conflict has improved the political fortunes of Ehud Barak, the defence minister, whose Labour party has climbed in opinion polls this week to a stronger third position.

The foreign minister, Tzipi Livni, of the Kadima party, has now drawn level in the polls with Binyamin Netanyahu, the Likud opposition leader, who had been a clear favourite to win February's general elections.