Graphic: white phosphorus | How The Times broke the story | Photographic evidence | Spent shells prove use | The burn victims | War in Gaza photojournalism

Israeli forces shelled the headquarters of the United Nations Relief and Works Agency with phosphorus bombs and artillery rounds yesterday, setting fire to the compound and destroying food and humanitarian supplies, officials said.

Thick smoke was still billowing from the building in Gaza City last night as UNRWA workers and firefighters struggled to salvage the food worth millions of pounds. The compound had been used to shelter hundreds of people fleeing Israel’s 20-day offensive in Gaza. Israeli officials said that an end to the fighting was in sight despite the recent escala-tion of the ground offensive.

Chris Gunness, of the UN agency, said: “What more powerful symbol can there be than pallets used for aid being set alight by the fighting? With white phosphorus you cannot put out the flames with water. You need sand, and there is too much fighting for our staff to get sand.” The Israeli military denies using white phosphorus shells, although an investigation by The Times has revealed that dozens of Palestinians in Gaza have sustained serious injuries from the substance, which burns at extremely high temperatures.

Gordon Brown condemned the attack as indefensible. He said: “The intensification of Israeli military action, and continued Hamas rocket attacks, reinforce the urgency of our call for an immediate ceasefire.”

The UN agency, which looks after four million Palestinian refugees in the region, suspended its operations in Gaza after the attack, in which three of its staff were injured. Amnesty International called for an immediate investigation into the shelling and Israel’s apparent use of white phosphorus. “[It] is an incendiary weapon which should never be used in densely populated civilian areas due to its devastating effects,” Malcom Smart, a director of the group, said.

Ban Ki Moon, the UN Secretary-General, who is in the region to put pressure on Hamas and Israel to reach a ceasefire agreement, demanded a full investigation.

Ehud Olmert, the Israeli Prime Minister, said that the military had fired artillery shells at the UN compound after Hamas militants opened fire from inside it. “It is absolutely true that we were attacked from that place, but the consequences are very sad and we apologise for it. I don’t think it should have happened and I’m very sorry,” Mr Olmert said.

The shelling came as Israeli forces struck deep into Gaza’s urban centres, pushing farther into the city and hitting two hospitals. At least 15 Palestinians were killed, medical officials said, pushing the death toll towards 1,100.Israeli officials said that they had killed Said Siam, one of Hamas’s top five leaders in Gaza. Hamas fired twenty rockets at southern Israel, injuring ten Israelis, including two wounded when a rocket hit a car in the city of Beersheba.

The Egyptian-brokered ceasefire talks continued in Cairo yesterday, with Hamas saying that it would agree to a year-long renewable ceasefire in Gaza if Israel pulled out all its forces within five to seven days and reopened border crossings immediately. Neither side would say how close they were to reaching an agreement.

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