GAZA CITY, Jan 15: Israel shelled the United Nations headquarters in the Gaza Strip on Thursday, engulfing the compound and a warehouse in fire, destroying thousands of pounds of food and humanitarian supplies intended for Palestinian refugees and triggering world condemnation and protests at the attack.

UN workers and Palestinian fire-fighters, some wearing bullet-proof jackets, struggled to douse the flames and pull bags of food aid from the debris after the attack.

In another air strike, Israel killed senior Hamas Interior Minister Said Siam along with his brother and son, Hamas said.

Separately, Israeli planes hit a UN school in another Gaza City neighbourhood, wounding 14 people who had sought sanctuary there, medics and fire-fighters said.

Said Siam was slain along with his brother and son in the Israeli air strike on his brother’s house north of Gaza City, Hamas said, as it vowed to avenge its leader’s death.

UN Secretary-General Ban Ki-moon, who is in the region to end Israel’s devastating offensive against Gaza, demanded a “full explanation” of the air strike on the UN HQ and said the Israeli defence minister told him there had been a “grave mistake.”

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

John Ging, director of UNRWA operations in Gaza who was in the compound at the time, dismissed the Israeli account as nonsense and said the attack at the compound caused a massive explosion, wounding three people.

France denounced the latest attacks.

“We condemn in the strongest terms the bombings this morning by the Israeli army of several hospitals and a building housing international media in Gaza city,” said French foreign ministry spokesman Eric Chevallier.

British Prime Minister Gordon Brown condemned the violence on both sides.

“Today’s attack on the UN headquarters in Gaza is indefensible,” he said.

“The intensification of Israeli military action, and continued Hamas rocket attacks, reinforce the urgency of our call for an immediate ceasefire.”

EU’s Czech presidency said the Israeli attack on a UN compound was simply unacceptable, demanding that the Jewish state take measures to prevent any recurrence.

The EU presidency “condemns today’s strike on a building of UNRWA in Gaza City by Israeli artillery,” a statement said.

“The (EU) Presidency demands that Israel undertake measures to prevent any recurrence of this attack on civilian or humanitarian targets, which is simply unacceptable,” it added.

EU Humanitarian Aid Commissioner Louis Michel said: “It is unacceptable that the UN headquarters in Gaza has been struck by Israeli artillery fire.”

Greece strongly protested to Israel after its navy turned back a boat chartered by Greek activists to take medical aid to the Gaza Strip, the foreign ministry said.

The boat was carrying several tonnes of medical supplies.

In Strasbourg, the European Parliament denounced the Israeli blockade preventing aid from arriving in Gaza.

Iranian President Mahmoud Ahmadinejad strongly condemned the genocide of Palestinians in Gaza and accused some Arab and Islamic states of complicity in the Israeli attacks.

Even as a top Israeli envoy went to Egypt to discuss a cease-fire 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.

Despite fierce Israeli offensive, defiant Hamas militants continued to launch projectiles on Thursday, sending two long-range Grad missiles crashing into the southern Israeli city of Beersheva and wounding five people, medics said.—Agencies