An injured Palestinian is helped from the rubble following an Israeli missile strike in Rafah, southern Gaza Strip, Saturday, Dec. 27, 2008. Israeli warplanes retaliating for rocket fire from Gaza pounded dozens of security compounds across the Hamas-ruled territory in unprecedented waves of air strikes Saturday, killing at least 155 and wounding more than 310 in the bloodiest day in Gaza in decades.

Crawford, Texas ? The U.S. on Saturday blamed the militant group Hamas for breaking a cease-fire and attacking Israel, which retaliated with strikes of its own during what became the single bloodiest day of fighting in years.

The White House called for the cease-fire to be restored, yet there were few indications that the violence, which has left more than 200 people dead and nearly another 400 wounded, was waning. Israeli Defense Minister Ehud Barak warned that the operation in Gaza would widen if necessary.

It was “completely unacceptable” for Hamas, which controls Gaza, to launch attacks on Israel after a truce lasting several months, said Gordon Johndroe, a spokesman for the National Security Council.

“These people are nothing but thugs, so Israel is going to defend its people against terrorists like Hamas that indiscriminately kill their own people,” Johndroe said in Texas as President George W. Bush was spending the week before New Year’s at his ranch here. “They need to stop. We have said in the past that they have a choice to make. You can’t have one foot in politics and one foot in terror.”

President-elect Barack Obama was receiving an intelligence briefing on Saturday from various security agencies, Johndroe said. Bush has spoken to regional leaders and the administration will remain in close contact, he said.

Obama also spoke during the day with Secretary of State Condoleezza Rice, who was keeping Bush abreast of the situation.

Brooke Anderson, Obama’s national security spokeswoman, said Saturday that Obama “is closely monitoring global events, including the situation in Gaza, but there is one president at a time.”

As Israel bombed Gaza, defiant Hamas leaders threatened revenge. Hamas “will continue the resistance until the last drop of blood,” vowed spokesman Fawzi Barhoum.

Moderate Palestinian President Mahmoud Abbas, who controls the West Bank, condemned Israel. Egypt summoned the Israeli ambassador to express condemnation and opened its border with Gaza to allow ambulances to drive out some of the wounded.

Asked if the United States would back a continuation of the retaliatory strikes by Israel, Johndroe said: “The U.S. doesn’t want to see any more violence. I think what we’ve got to see is Hamas stop firing rockets into Israel. That’s what precipitated this.”

At his ranch, the president took a call from King Abdullah of Saudi Arabia, who wanted to discuss the violence that began eight days after a six-month truce between Israel and the militants expired.

“The United States strongly condemns the repeated rocket and mortar attacks against Israel and holds Hamas responsible for breaking the cease-fire and for the renewal of violence in Gaza,” Rice said in a statement. “The cease-fire should be restored immediately. The United States calls on all concerned to address the urgent humanitarian needs of the innocent people of Gaza.”