The White House is condemning the bombing in the Iraqi city of Najaf that killed at least 75 people, including a leading Shi'ite Muslim cleric.

White House spokeswoman Claire Buchan deplored what she calls "this act of terrorism" and says President Bush sends his condolences to those who lost loved ones in the bombing.

She says the Bush administration remains determined to defeat terrorism and will continue to work toward bringing a better life to the Iraqi people following the U.S.-led invasion that toppled Saddam Hussein.

Officials in neighboring Iran blame the U.S. "occupation force" for the attack, saying those soldiers are ultimately responsible for security in Iraq.

Democrats and Republicans in the U.S. Congress have been calling for more troops to improve security there as U.S. soldiers continue to come under attack.

The number of soldiers killed since the president declared an end to major combat operations four months ago now exceeds the number of deaths recorded during the invasion itself.

The Bush administration says troop levels at present are "appropriate," though officials say they will continue to work with U.S. military and civilian authorities in Iraq to make sure they have the resources to "get the job done."