Reports say the Imam Al-Mahdi Army, loyal to nationalist Shi'ite cleric Muqtada al-Sadr, had asked police for help in recovering a comrade who was being held. The group was attacked by insurgents as they prepared to launch the operation.
There was no immediate information on casualties on the insurgent side.
In a separate incident, the U.S. military says two soldiers were killed yesterday when their convoy struck an improvised explosive device in east Baghdad.
The Ukrainian Defense Ministry, meanwhile, said today that three Ukrainian peacekeepers in Iraq were injured in a land-mine accident. They were hospitalized and listed in stable condition.
For the latest news and analysis on Iraq, see RFE/RL's webpage on "The New Iraq" .