At least 435 people killed, 2,150 wounded as Israeli attacks on Gaza continue.
Israeli warplanes continued to pound Gaza on Saturday as the assault on Hamas entered its second week, with the Islamist group's leader warning of a "black destiny" if ground troops are sent in.
An Israeli army spokeswoman said the air assault was continuing into the early hours of Saturday, but would not provide any details.
Hamas's Syrian-based chief Khaled Meshaal told Israel that "if you commit the stupidity of launching a ground offensive then a black destiny awaits you.
"You will soon find out that Gaza is the wrath of God," Meshaal said in pre-taped remarks as the death toll rose from bombing and concerns grew about the humanitarian situation in the Hamas-ruled Palestinian territory.
The United States gave Israel free rein on whether to invade the overcrowded enclave, insisting that the key to a ceasefire is Israel's demand for Hamas to permanently halt rocket fire.
"So I think any steps they are taking, whether it's from the air or on the ground or anything of that nature, are part and parcel of the same operation," said White House spokesman Gordon Johndroe.
"Those will be decisions made by the Israelis."
President George W. Bush, meanwhile, urged all able parties to press Hamas to stop firing on Israel to facilitate a lasting ceasefire.
"The United States is leading diplomatic efforts to achieve a meaningful ceasefire that is fully respected," Bush said in his weekly Saturday radio address, the text of which was released late on Friday.
"I urge all parties to pressure Hamas to turn away from terror, and to support legitimate Palestinian leaders working for peace."
Bush said Hamas was responsible for the latest violence and rejected a unilateral ceasefire that would allow Hamas to continue to fire on Israel.
"This recent outburst of violence was instigated by Hamas - a Palestinian terrorist group supported by Iran and Syria that calls for Israel's destruction," Bush said.
Israeli Prime Minister Ehud Olmert met with senior ministers as tanks and troops stood at the ready on the Gaza border.
A missile fired by an Israeli jet slammed into a house in southern Gaza, killing three boys, aged from seven to 10. It was one of more than 58 fresh raids carried out on Friday.
A 12-year-old girl died of her wounds after the bombing of a house near Gaza City belonging to a member of Islamic Jihad, and two gunmen from the armed wing of Hamas were killed in Jabaliya after firing rockets, medics said.
Since Israel unleashed its campaign on December 27 in response to persistent rocket fire, at least 435 people have been killed, including 66 children, and 2,150 wounded, according to Gaza medics.
The bombardment has demolished dozens of houses and heightened concern over the humanitarian situation in Gaza, where most of the 1.5 million residents depend on foreign aid.
"The protection of civilians, the fabric of life, the future of the peace talks and of the regional peace process has been trapped between the irresponsibility of the Hamas attacks and the excessiveness of the Israeli response," Robert Serry, the UN envoy for the Middle East, told reporters in Jerusalem.
Max Gaylard, the UN humanitarian coordinator for the Palestinian territories, said "there is a critical emergency in the Gaza Strip right now ... By any definition this is a humanitarian crisis and more."
Thousands of Hamas faithful attended the funeral of Nizar Rayan - a firebrand hardliner who was killed with his four wives and 11 children on Thursday.
Hamas vowed to avenge the death of the most senior Hamas leader killed by Israel since Abdel Aziz al-Rantissi in 2004 and warned that it could resume suicide attacks against Israel for the first time since January 2005.
Thousands of protesters took to the streets of Gaza and the occupied West Bank after Hamas called for a "day of wrath." Police fired tear gas at rock-throwing youths in annexed east Jerusalem.
With a ground offensive widely expected and no ceasefire in sight, the Israeli army opened a border crossing to allow an estimated 400 people with foreign passports to leave Gaza.
Hamas fired more than 30 rockets into Israel, but no casualties were reported.
Militants have fired more than 360 rockets into Israel over seven days, killing four people and wounding dozens more.
The offensive has sparked angry protests in the Muslim world and elsewhere across the globe and defied diplomatic efforts to broker a truce.