But the White House said it has asked Israel to try hard to avoid civilian casualties as reserves were called up for an expected ground incursion on top of a week of air strikes that has killed more than 400 Palestinians.

"We've been in regular contact with the Israelis," White House deputy press secretary Gordon Johndroe told reporters when asked if US officials were trying to prevent a possible ground offensive.

US officials have urged the Israelis "to be mindful that any of the actions that they're taking in Gaza avoid unnecessary civilian casualties and also to help continue with the flow of humanitarian goods," he said.

"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," Johndroe said.

"Those will be decisions made by the Israelis," he said.

"Israel has a right to defend itself from these rocket attacks, and so we'll see," Johndroe said when asked about progress toward a ceasefire.

After briefing Bush about events in Gaza, just 18 days before he hands the White House to his successor Barack Obama, Secretary of State Condoleezza Rice said Washington was pursuing diplomacy with its partners in the Middle East.

"We are working toward a ceasefire that would not allow a re-establishment of the status quo ante where Hamas can continue to launch rockets out of Gaza," Rice told reporters outside the White House.

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

Rice repeated the US stand that any ceasefire must be a "durable" one, in contrast to the previous six-month agreement that expired on December 19.

Gordon Duguid, a State Department spokesman, added that Rice has since New Year's Day spoken to former British prime minister Tony Blair, the envoy for the Middle East quartet of the United States, Russia, the European Union and the United Nations.

She has also spoken since then to Israeli Prime Minister Ehud Olmert and her counterparts David Miliband of Britain, Sheikh Abdullah bin Zayed al-Nayhan of the United Arab Emirates, Salah Bashir of Jordan and Ahmed Abul Gheit of Egypt, he said.

Duguid said she also spoke Friday to Karel Schwarzenberg, the foreign minister of the Czech Republic, which has assumed the rotating presidency of the European Union.

In the last week Rice has spoken with counterparts Tzipi Livni of Israel, Saud al-Faisal of Saudi Arabia, Javier Solana of the European Union and King Abdullah II of Jordan.

Rice again pinned the blame for the violence on Hamas, the Islamist Resitance Movement that seized power in Gaza in June 2007 after ousting the US-backed Palestinian Authority of Mahmud Abbas.

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, launched a week ago on Saturday in response to a wave of rockets fired from Gaza, has killed at least 422 people and wounded more than 2,100 others.

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

"Arab opinion, I hope will understand what we're trying to do. I understand that passions in the region are inflamed by the situation," Duguid said when asked if the US was concerned about Arab reaction.

"I only can offer them our sincerest efforts to try and work with our partners to achieve a ceasefire and move on and achieve a political settlement," he said.

He said a political dialogue was possible with Israel if Hamas renounces violence and recognizes Israel's right to exist.

Duguid added that the United States arranged for 27 people who are US citizens and their immediate family members to leave the Gaza Strip and travel to Amman, Jordan.