The U.S. military says Iraqi Army troops captured a "high-level insurgent" during a raid in an eastern Baghdad neighborhood early Friday.
A statement said the suspect headed "multiple insurgent cells in Baghdad" that had attacked Iraqi and coalition forces with roadside bombs and car bombs. It did not identify the man.
The statement says the raid sparked a gunbattle, and an estimated 30 to 40 enemy fighters were killed or wounded in the 43-minute firefight.
The military says there were no casualties among Iraqi or coalition forces.
Earlier, Iraqi police reported nine people were killed and 14 wounded in the fighting at Sadr City - a slum dominated by anti-American Shi'ite cleric Moqtada al-Sadr and his Mehdi Army blamed for increasing sectarian violence in the country.
The U.S. military said the raid was part of an ongoing operation to stem continuing violence in Baghdad and capture insurgent leaders.
Other insurgent bombings and mortar attacks on Sunni Arab mosques in Baghdad today killed at least five people.
In another development Thursday, a former U.S. soldier, Army Private Steven Green, facing charges of raping and murdering an Iraqi woman and killing three members of her family pleaded not guilty at a U.S court in the state of Kentucky.
Other U.S. soldiers are under investigation in the case.
Senior U.S. diplomatic and military officials in Iraq have pledged to hold American service members accountable if they are found guilty of misconduct.
Iraqi Prime Minister Nouri al-Maliki repeated his call for an independent inquiry into the allegations.
Some information for this report was provided by AFP, AP and Reuters.