Iraqi troops on Thursday arrested the top official in Amarah, a Muqtada al-Sadr loyalist, officials said, drawing swift condemnations from followers of the anti-U.S. cleric and raising tensions as a military operation against Shiite militias got under way.

Rafia Abdul-Jabbar, who also was acting deputy governor for Maysan province, was seized from his office Thursday morning along with a member of the provincial council, a local official said.

The arrest came as Iraqi troops fanned out and gunmen tossed weapons on the streets or in canals with the official launch of the military crackdown in Amarah, a stronghold of al-Sadr's Mahdi Army militia and the purported center of weapons smuggling from neighboring Iran.

The military action came a day after the expiration of a four-day deadline for militants in Amarah to surrender their arms or face arrest.

It's the fourth such U.S.-backed Iraqi military operation launched against Shiite and Sunni extremists in recent months as Prime Minister Nouri al-Maliki seeks to assert government control over the country ahead of provincial elections to be held in the fall.

The Sadrists have accused the Shiite-led government of trying to undermine the movement ahead of the vote, which is expected to redistribute more power among their bloc and Sunni parties who boycotted the last provincial vote in January 2005.

The Iraqi Defense Ministry spokesman Maj. Gen. Mohammed al-Askari told AP Television News that Abdul-Jabbar was among 17 wanted people detained Thursday morning.

Sadrist officials said the arrest violated the spirit of agreements made in talks with the government in the run-up to the operation. The Sadrists had promised not to resist the operation as long as Iraqi troops did not make arrests without warrants or commit other violations.

"We were surprised by the violations and the random raids in Amarah," said Hazim al-Araji, a senior al-Sadr aide in the holy city of Najaf. "We condemn the latest events that show a deliberate targeting of al-Sadr's movement."

Al-Araji said he suspected some officers were linked to rival Shiite parties and were "trying to create a crisis and a tension through these operations."

"We were so surprised to hear of the arrest of the mayor. He was very cooperative and working to make the plan a success," al-Araji said.

In announcing the start of the operation, the government said Col. Mahdi al-Assadi, the provincial police commander, has imposed an indefinite curfew on parts of the city but said government offices, schools and colleges won't be affected.

Iraqi security forces already have found large weapons caches and munitions in the run-up to the offensive, it said.

About 30 gunmen handed in weapons, while others were randomly throwing them in the streets or in canals to avoid arrest, the provincial spokesman said, speaking on condition of anonymity because he wasn't authorized to release the information. He added that large weapons caches had been found hidden outside the city.

In a bid to shore up support among the local populace, recruiting centers for the Iraqi police and the army were opened in the city center.

Iraqi army reinforcements began arriving last week in Amarah, 200 miles southeast of Baghdad, to prepare for the operation, but no fighting has been reported.

The Amarah operation comes as U.S. and Iraqi troops continue offensives against Shiite militias in the southern city of Basra and Baghdad's Sadr City district as well as against Sunni insurgents in the northern city of Mosul.

Iraqi troops arrested 11 people on the wanted list who were believed be members of armed groups and seized an unspecified number of weapons during overnight raids in Basra, Iraqi military commander Maj. Gen. Mohammed Jawad Huwaidi told The Associated Press.

U.S. troops also captured six suspected insurgents, including a wanted man believed to have ties to local Al Qaeda in Iraq leaders, the military said. Fifteen others were captured during operations targeting Al Qaeda elsewhere in northern Iraq, according to the statement.