BAGHDAD — A suicide bomber detonated his explosives belt in a line of Shiite worshippers near the entrance of a mosque south of Baghdad during prayer services today, killing at least nine people, Iraqi officials said.

The attacker struck around noon while waiting in a line to be searched outside 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 today. 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 ceasefire 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. Today's s bomber struck a mosque run by al-Sadr loyalists in Musayyib, 40 miles south of Baghdad.

Nobody claimed responsibility for the attack but suicide bombers are the signature attack of the group al-Qaida in Iraq.