A homicide bomber struck a Shiite mosque south of Baghdad during Friday prayer services, killing at least nine people, Iraqi officials said.

The attacker detonated his explosives belt around noon as he waited in a line to be searched at the entrance of the mosque in Musayyib, a police officer said, speaking on condition of anonymity because of security concerns.

The blast came a day after Iraqi lawmakers approved a security pact with the United States that will allow U.S. forces to stay in Iraq for three more years. Proponents of the deal — which still must be ratified by the three-member presidential council — argued the Americans are still needed because Iraqis aren't ready to take over security.

Anti-U.S. cleric Muqtada al-Sadr called for peaceful protests over the agreement in a statement Friday. But in a significant omission, he did not repeat his threat to unleash militia fighters to attack U.S. forces if they don't leave immediately.

Al-Sadr also urged his followers to close his offices and affiliated institutions for three days "to show the tragedy that has befallen us," according to the statement that was read to reporters by his spokesman Sheik Salah al-Obeidi.

"We offer our condolences to the Iraqi people over this calamity that has fallen upon them with the signing of the agreement of humiliation and indignity," it said. "We will keep on calling for continuous peaceful public protests."

A cease-fire order by the Shiite cleric, who is believed to be in Iran, has been a key factor in the drop in violence over the past year.

Friday's homicide bomber struck a mosque run by al-Sadr loyalists in Musayyib, 40 miles south of Baghdad.

The police officer said the nine killed included a woman who was begging nearby. Dr. Saad al-Janabi confirmed the casualty toll, saying 15 people also were wounded.

Nobody claimed responsibility for the attack but homicide bombers are the signature attack of al-Qaeda in Iraq. The U.S. military has warned Sunni insurgents are trying to provoke revenge attacks by Shiite extremists.

Under the pact, U.S. forces will withdraw from Iraqi towns and cities by June 30 and the entire country by Jan. 1, 2012.

Iraq also will have strict oversight over the nearly 150,000 American troops now on the ground, representing a step toward full sovereignty for Iraq and a shift from the sense of frustration many Iraqis feel at the presence of U.S. troops on their soil for so many years.