BAGHDAD, Iraq — Prime Minister Nouri al-Maliki threatened to block the party of radical cleric Muqtada al-Sadr from upcoming provincial elections as clashes between rival Shiite factions continued yesterday in Baghdad. At least three American soldiers were killed in the capital yesterday in two attacks, the military said. Two were killed by rocket-propelled grenades, and one was fatally shot after a roadside bomb struck the convoy in which he was traveling, the military said. News of their deaths came a day after four American soldiers died in other attacks in the country.

The prime minister said in an interview with CNN that Mr. al-Sadr must disband the Mahdi Army, his powerful militia, in order to participate in elections scheduled for October.

A top aide to al-Sadr, Hassan al-Zargani, said the cleric is willing to disband the militia if his religious leaders sign off on the move, and if the Iraqi government meets certain unspecified conditions. “The government should give a number of guarantees,” Mr. al-Zargani said, “because dissolving the army is not an easy thing to do.”

Mr. Maliki described a bloody offensive targeting Shiite militias in Basra late last month as successful and said the operation had empowered the government to pursue militias elsewhere in the country.

“The state came out with the maximum power, nationalism, popular, and national support that expressed itself, and for the first time, the one who is cornered and defeated is this gang,” Mr. Maliki said, according to a transcript of the interview posted on CNN’s Web site.

The Mahdi Army had maintained a low profile in recent months following a cease-fire Mr. al-Sadr declared last August. The cease-fire was broken after the Basra offensive, and the militia has since clashed repeatedly with American-backed Iraqi forces.

An Iraq expert at the U.S. Peace Institute who worked in Iraq last year advising the parliament on rule of law and constitutional issues, Jason Gluck, said disbanding the militia would be a gamble for Mr. al-Sadr. The move could broaden his standing as a national leader and make him an attractive ally for Sunni groups eager to create an opposition bloc. But it could also weaken him.

“Until now, Sadr has enjoyed influence in Iraq that was disproportionate to his popular support because of his militia,” Mr. Gluck said. “He was able to exist both within and outside the political arena because Maliki permitted him to do so. He cannot, however, survive for long with both Maliki and the Americans going full tilt against him.”