Israel shelled the United Nations headquarters in the Gaza Strip on Thursday. The compound and a warehouse were engulfed in flames, destroying thousands of pounds of food and humanitarian supplies intended for Palestinian refugees. Israel's prime minister, Ehud Olmert, said that there had been a "grave mistake."

UN Secretary-General Ban Ki-moon is in the region in an attempt to end the devasting offensive actions against Gaza's Hamas rulers by Israel. Ban Ki-moon demanded a "full explanation", and revealed that Olmert said it was a mistake.

UN workers and Palestinian firefighters worked side-by-side, some wearing bulletproof vests, in a struggle to put out the flames and retrieve bags of food from the debris.

Prime minister Olmert said that the military fired artillery shells at the UN headquarters after Hamas militants opened fire from the location. Three people were wounded in the attack. A senior military official from Israel also explained that Israel troops shelled the compound after coming under fire from Palestinian militants there. A UN official there at the time, however, dismissed these reports as "nonsense."

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

The Israeli military continued to push further into Gaza, in what appears to be an attempt to increase pressure on Hamas. Shells struck a hospital, five high-rise apartment buildings, and a building that houses media outlets in Gaza City. Several journalists were injured. Ground forces also thrust deep into a crowded neighborhood for the first time, sending terrified residents running for cover.