BAGHDAD (AP) – U.S. troops captured an alleged Shiite militia leader and three other suspects in a raid south of Baghdad, the U.S. military said Friday.

The operation took place late Thursday in the Mashru area, the military said in a statement. The main suspect, it said, was believed to be a “special groups” leader, language the military uses to describe Shiite Muslim militias allegedly backed by Iran. The U.S. says the groups have broken ranks with Muqtada al-Sadr’s Mahdi Army. The radical cleric in August called a six-month cease-fire, which is due to expire later this month.

The U.S. has been careful not to accuse al-Sadr himself of any role in ongoing attacks, and instead blame rogue militiamen violating his cease-fire order. Nevertheless, U.S. and Iraqi officials have been cracking down on al-Sadr’s followers, especially in Shiite holy cities south of Baghdad.

The military identified the main suspect in Thursday’s raid as “a deputy for special groups criminal elements in Wasit province,” and “a close associate of several senior-level criminal element leaders involved in attacks” on U.S. and Iraqi forces. He and three others were captured without incident, the military said.

The arrests came hours after al-Sadr’s office issued a statement warning Mahdi Army fighters to stick with his cease-fire order, after U.S. and Iraqi raids earlier Thursday in Baghdad’s Sadr City, the main Shiite district and Mahdi Army bastion.

In the statement, al-Sadr threatened to expel militiamen from his group who break the cease-fire. The order is credited with helping tamp down violence dramatically in Baghdad, along with the arrival of about 30,000 U.S. reinforcements last summer.

Al-Sadr has threatened not to extend the cease-fire unless the government purges rival Shiite militiamen he alleges have infiltrated the security forces and are targeting his followers.

Fifteen suspected militants were detained in Thursday’s sweeps through Sadr City, and one person was killed. The U.S. similarly said it was targeting “criminal elements” responsible for attacks with mortars and powerful roadside bombs that the Pentagon links to Iranian aid.

On Friday, mourners gathered at the Sadr City home of Arkan Abid Ali, who died of wounds sustained during the U.S. operation there a day earlier. The 22-year-old was shot in the chest, and later died at a U.S. military hospital, U.S. and Iraqi officials said. His body was transferred to Iraqi officials early Friday, and a funeral procession was under way. Ali would be buried later in the day in the Shiite holy city of Najaf, police said.

In a separate statement issued Friday, the military said rogue militiamen continue to launch “hit and run attacks” on U.S. and Iraqi forces from Sadr City.

There were at least six attacks on American troops in two sections of Sadr City during the first three days of February, the military said. And U.S. soldiers conducting mounted patrols near the Shiite neighborhood came under fire twice last weekend, it said.

“The soldiers were not able to positively identify the shooters in either case, and consequently did not return fire in order to avoid harming Iraqi civilians,” it said. In other violence, Iraqi police said a roadside bomb killed three awakening council members and wounded eight others Thursday south of Baghdad.

Such councils are comprised of mostly Sunni tribesmen who have partnered with American forces to oust al-Qaeda and other militants from their hometowns.

The attack occurred along a road leading into Madain, a predominantly Sunni town about 20 kilometers (14 miles) southeast of the capital.