ISRAELI shells set ablaze a food warehouse at UN headquarters in Gaza yesterday, destroying tons of emergency rations intended for needy Gaza civilians, a senior UN official said.
A pall of black smoke rose from the UN compound, visible across Gaza City. Flour spilled on the ground and mixed with soot as Palestinian firefighters tried to douse the flames.

"The main warehouse was badly damaged by what appeared to be white phosphorus shells," UN humanitarian affairs chief John Holmes said at a news briefing in New York.

"Those on the ground don't have any doubt that's what they were. If you were looking for confirmation, that looks like it to me." The compound belongs to the UN Relief and Works Agency for Palestine Refugees (Unwra).

The rights group Human Rights Watch has accused Israel of using white phosphorus, which can create smoke screens or mark targets but also makes a devastating incendiary weapon.

Israel's prime minister, Ehud Olmert, said the military fired artillery shells at the UN compound after Hamas militants opened fire from the location, a version of events John Ging, director of Unwra in Gaza, rejected as "nonsense"

Mr Ging said Israeli shells first hit a courtyard filled with refugees, then struck garages and the UN's main warehouse, sending thousands of tons of food aid up in flames. Later, fuel supplies ignited, sending a thick plume of smoke into the air.

"It's a total disaster for us," said Mr Ging, adding that the UN had warned the Israeli its shelling put the compound in danger.

Ban Ki-moon, the UN secretary-general, who is in the region to encourage a ceasefire, demanded a "full explanation" and said the Israeli defence minister, Ehud Barak, had told him there had been a "grave mistake".

Gordon Brown, the Prime Minister, called the attack "indefensible", saying the UN's mission in Gaza "is purely humanitarian, bringing relief to civilians suffering in appalling conditions as a result of the ongoing military actions and restrictions on food and medical supplies entering Gaza".

Even as a top Israeli envoy went to Egypt to discuss a cease-fire proposal, the military pushed further into Gaza in an apparent effort to step up pressure on Hamas. Ground forces thrust deep into a crowded neighbourhood for the first time, as terrified residents fled.

The compound of al-Quds hospital, in the Tel Huwa area of Gaza City, where Israeli troops advanced yesterday, also came under Israeli shelling. A shell hit a building connected to the hospital belonging to the Red Crescent Society and another crashed into the pharmacy on the second floor of the hospital building. Firefighters were able to prevent the fire reaching the main hospital building, paramedic Adil al-Azbat told The Scotsman.

"We put the patients on the underground floor where the surgical department is. There was great fear, great terror, an inability to concentrate. We felt at this moment that the hospital is on the brink of destruction," he added.

Meanwhile, an air strike in Gaza City killed a senior Hamas leader, Sayyid Siyam, interior minister in Gaza's government. Mr Siyam was a key figure in Hamas, and oversaw the militiamen who seized control of the Gaza Strip during the June 2006 armed takeover from forces loyal to the Palestinian Authority president, Mahmoud Abbas.

A total of 1,076 Palestinians have died in the Israeli offensive, which began to prevent rocket fire from the Strip into Israel.

At least 670 of them are civilians, according to Palestinian rights groups.

A total of 13 Israelis have died either from missile strikes on southern Israel or in the fighting in Gaza.