GAZA CITY - Warplanes pounded Gaza for a fourth day on Tuesday as tanks stood by to join the "all-out" war Israel vowed, and the Palestinian death toll rose to at least 360.
Israel made it clear Monday the offensive was just beginning, even as UN chief Ban Ki-moon urged world leaders to work urgently to end the "unacceptable" violence.
Palestinian resistance fighters responded to Israeli air strikes with deadly rocket and mortar fire that has so far killed four Israelis.
Defence Minister Ehud Barak, who has threatened to launch ground incursions alongside the aerial blitz, said Israel is in "an all-out war with Hamas."
Deputy Prime Minister Haim Ramon said the offensive's goal "is to topple Hamas."
With Israeli tanks just metres (yards) away from Gaza, the army decreed the border area a closed military zone -- a move that in the past has been followed by ground operations.
"After this operation there will not be a single Hamas building left standing in Gaza, and we plan to change the rules of the game," said armed forces deputy chief of staff Brigadier General Dan Harel, quoted by the YNet News website.
At least 57 Palestinian civilians, including 21 children, have been killed in the Israeli bombardment, a UN spokesman said.
Israeli aircraft carried out dozens of air strikes under the cover of darkness early Tuesday, sources and witnesses said.
The attacks completely destroying the Hamas foreign and finance ministry buildings along with nearby homes, and set off fires, witnesses said.
At least 10 Palestinians were killed and 40 wounded in the latest attacks, the director of Gaza's emergency services, Moawiya Abu Hassanein said.
In all, the Israeli campaign has killed at least 360 Palestinians and wounded more than 1,690, he said.
Since the onslaught began on Saturday, Gaza militants have fired more than 250 rockets and mortar rounds into Israel, killing four people and wounding two dozen more.
As the fighting continued the White House signalled strong support for Israel.
"The United States understands that Israel needs to take actions to defend itself," said spokesman Gordon Johndroe.
But at the United Nations, Ban said he was "deeply alarmed by the current escalation of violence in and around Gaza. This is unacceptable.
"Both Israel and Hamas must halt their acts of violence and... a ceasefire must be declared immediately."
He chided leaders, saying: "I think regional and international partners have not done enough. They should do more."
The UN special envoy to the Middle East on Monday also protested strongly to Israel after air strikes on Gaza hit two UN buildings and killed eight of its trainees.
There was also growing concern about the humanitarian situation in the aid-dependent territory of 1.5 million which Israel has virtually sealed off in June 2007.
Anger in the Muslim world is spiralling. Turkey announced it had suspended brokering preparatory peace negotiations between Syria and Israel because of the air assault as protests intensified worldwide.
Parliament in Jordan -- one of two Arab states to have signed a peace treaty with Israel -- demanded that the government "reconsider" relations with the Jewish state.
Palestinian president Mahmud Abbas, whose forces were ousted from Gaza in the Hamas takeover, implored the international community to help end "this aggression."
Hamas, which won in 2006 Palestinian parliamentary elections, lashed out at the world for not doing enough to end the blitz.
Israel is "committing a holocaust as the whole world watches and doesn't lift a finger to stop it," spokesman Fawzi Barhum told reporters.
Bahrain clamps down on Shiite activists