His administration meanwhile gave Israel free rein over whether to send ground troops into Gaza, despite growing criticism over its handling of a conflict that has killed at least 435 people, including 66 children.

"The United States is leading diplomatic efforts to achieve a meaningful ceasefire that is fully respected," Bush said in his weekly radio address, the text of which was released by the White House in advance.

These were his first remarks since the conflict erupted a week ago.

He said "I urge all parties to pressure Hamas to turn away from terror, and to support legitimate Palestinian leaders working for peace," including Mahmud Abbas, president of the US-backed Palestinian Authority.

He said he has been in contact with Abbas as well as King Abdullah Bin Abdulaziz of Saudi Arabia, King Abdullah II of Jordan, President Hosni Mubarak of Egypt, Prime Minister Ehud Olmert of Israel.

Bush, who hands the White House to his successor Barack Obama in just 18 days, blamed Hamas for the latest violence and rejected a unilateral ceasefire that would allow Hamas to continue to attack Israel from the Gaza Strip.

Hamas shared power with the Palestinian Authority for a period after winning parliamentary elections in the West Bank and Gaza in 2006 but the arrangement collapsed and Hamas seized power outright in Gaza in June 2007.

"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.

Bush said the Israeli strikes were in self-defense after Hamas let a six-month ceasefire lapse on December 19 and fired rockets at Israel.

He also accused Hamas of putting Palestinian lives at risk by hiding among them.

White House deputy press secretary Gordon Johndroe earlier said the United States has urged Israel to avoid civilian casualties in their military operations, whether they involve continued air assaults or a ground incursion.

"Those will be decisions made by the Israelis," he said when asked if Israel would be justified in launching a ground assault.

Israel has thousands of troops massed for a ground offensive on Gaza that would aim to deal a hammer blow to Hamas and re-establish Israel's military credentials with its other foes, experts said.

After briefing Bush earlier, Secretary of State Condoleezza Rice said Washington sought a "ceasefire that would not allow a re-establishment of the status quo ante where Hamas can continue to launch rockets out of Gaza."

She added: "It is obvious that ceasefire should take place as soon as possible, but we need a ceasefire that is durable and sustainable."

Rice has had a flurry of consultations with her counterparts from Israel, Arab countries as well as Russia, Britain and the European Union, officials said. Johndroe added that Rice has also spoken to Obama in the last week.

Asked if she planned to travel to the Middle East to broker an end to the crisis, Rice replied: "I have no plans at this point."

The Israeli offensive has killed at least 435 Palestinians, including 66 children, and wounded 2,150 others, according to Gaza medics.

It has prompted condemnation from around the world, but particularly from Arab and Muslim countries.

In New York, Amnesty International sent a letter to Rice berating the administration for its "lopsided" support for the Israeli assault and urged it to suspend weapons deliveries to Israel.

Zbigniew Brzezinski, who was national security adviser for US president Jimmy Carter, told CNN television that Rice's remarks "clearly show that the US policy right now is completely bankrupt" and the Israeli offensive "will further radicalize the Palestinians."

He said Obama, whom he supports, will have to make a "fresh start" when he succeeds Bush on January 20.

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