GAZA CITY, Gaza Strip (AP):

Israel shelled the United Nations (UN) headquarters in the Gaza Strip yesterday, engulfing the compound and a warehouse in fire and destroying thousands of pounds of food and humanitarian supplies intended for Palestinian refugees.

Another Israeli bombardment yesterday killed the Hamas security chief.

UN workers and Palestinian firefighters, some wearing bulletproof jackets, struggled to douse the flames and pull bags of food from the debris after the Israeli attack, which was another blow to efforts to ease the humanitarian crisis in the Gaza Strip. Dense smoke billowed from the compound.

UN Secretary General Ban Ki-moon, who is in the region to end the devastating offensive against Gaza's Hamas rulers, demanded a "full explanation" and said the Israeli defence minister told him there had been a "grave mistake".

Consequences

Israeli Prime Minister Ehud Olmert said the military fired artillery shells at the UN compound after Hamas militants opened fire from the location. Three people were wounded.

"It is absolutely true that we were attacked from that place, but the consequences are very sad and we apologise for it," he said. "I don't think it should have happened and I'm very sorry."

Interior Minister Said Siam was killed in an Israeli air strike that flattened a home in Gaza City. Israel and Hamas both confirmed the death of Siam, who oversaw thousands of security agents and was considered to be among the militant group's top five leaders in Gaza.

Even as a top Israeli envoy went to Egypt to discuss a ceasefire proposal, the military pushed farther into Gaza in an apparent effort to step up pressure on Hamas. Ground forces thrust deep into a crowded neighbourhood for the first time, sending terrified residents fleeing for cover. Shells also struck a hospital, five high-rise apartment buildings and a building housing media outlets in Gaza City, injuring several journalists.