The United States is continuing diplomatic contacts for a Gaza cease-fire despite Israel's rejection of a French-proposed 48-hour truce. President Bush spoke with Israeli Prime Minister Ehud Olmert, who is said to have given an assurance Israel is trying to minimize civilian casualties in its air campaign against Hamas.

Officials here say the U.S. push for a durable and sustained Gaza cease-fire is continuing undaunted, despite the failure of the French bid to arrange a 48-hour truce for humanitarian relief efforts in the coastal strip.

Secretary of State Condoleezza Rice is taking the lead role in U.S. telephone diplomacy.

A spokesman said she had spoken three times in the last 24 hours with both Jordanian Foreign Minister Salah al-Bashir and Foreign Minister Sheikh Abdullah Bin Zayed al-Nahyan of the United Arab Emirates, a Gulf state having close contacts with Iran - a key sponsor of Hamas.

Meanwhile President Bush, spending the year-end holidays in Texas, telephoned Israeli Prime Minister Ehud Olmert to, among other things, voice concern about humanitarian conditions in Gaza. White House spokesman Gordon Johndroe said Mr. Olmert gave a renewed assurance Israel is targeting only Hamas and those affiliated with it.

"Prime Minister Olmert assured President Bush that Israel is taking appropriate steps to avoid civilian casualties," said Johndroe. "That was something the president asked for an update on, and President Bush got an assurance from Prime Minister Olmert that Israel is, as they have said they are doing, only targeting Hamas and that terrorist organization and people involved with Hamas, and that they are working to minimize any civilian casualties."

Johndroe said U.S. efforts are aimed at durable and lasting cease-fire in Gaza that is respected by Hamas - unlike the previous six-month truce that lapsed earlier this month and which he said the militant Islamic group had regularly violated with rocket fire into Israel.

He all those concerned want an end to the violence as soon as possible, but that the United States does not want to see it start up again in days and weeks with renewed rocket attacks.

The United States had avoided calling for an immediate cease-fire until Tuesday when it joined Russia, the European Union and the United Nations - its partners in the international Quartet on the Middle East - in a statement backing an immediate truce that is "fully respected" by both sides.

In a talk with reporters here, State Department Acting Spokesman Gordon Duguid said the Quartet's wording is critical.

"That formulation is what the Quartet has agreed upon," said Duguid. "You can't take and divide that sentence. They call for an immediate cease-fire that would be fully respected. We believe both sides should reach a cease-fire as quickly as possible but that cease-fire can't be one that is called immediate and then is immediately violated with rocket attacks by Hamas."

The State Department Wednesday renewed a call on U.S. citizens to avoid all travel to the Gaza strip and urged those already there to depart immediately.

U.S. diplomats and officials working in Israel have been told to avoid travel within a 30-kilometer radius of Gaza. Private Americans are being advised to keep even farther away from the conflict area, given the firing in recent days of longer-range rockets from Gaza.