Iraqi and U.S. forces battled Shi'ite militiamen in eastern Baghdad Friday, and the U.S. military said a "high-level insurgent" was captured in the operation.
Iraqi and U.S. officials say the insurgent was a Shi'ite commander in the Mehdi Army loyal to radical, anti-American cleric Moqtada al-Sadr. Shi'ite sources, however, say the commander appears to be still at large.
A U.S. military statement says 30 to 40 insurgents were killed or wounded in the fighting. The military says there were no casualties among Iraqi or coalition forces.
Iraqi authorities say nine insurgents were killed and about 30 wounded.
In other violence, a series of attacks against both Shi'ite and Sunni mosques killed at least 15 people and wounded more than 50 in the Baghdad area and in northern Iraq.
The attacks occurred shortly after Friday prayers and raised further fears of sectarian violence.
The deadliest bombing occurred in northern Iraq at a Shi'ite mosque near Sinjar in the village of Tal al-Banat. At least eight people were reported killed and more than 40 wounded.