A military statement said the raid involved air support, and targeted fighters who smuggle arms from Iran and facilitate the travel of Iraqi militants to Iran for training.
Twelve suspects also were detained. The U.S. statement came after Iraqi police reported U.S. air strikes had killed nine civilians in Al-Sadr City.
However, a U.S. military spokesman said there were no civilian casualties.
U.S. military officials say more than 70 percent of attacks carried out on U.S. forces in Baghdad in July were done by Shi'ite militias, some trained in Iran.
Al-Sadr supporters demonstrating against the U.S. presence in Iraq in October 2006 (epa)
A RADICAL CLERIC. Shi'ite cleric Muqtada al-Sadr is a key figure in Iraq. He heads the Imam Al-Mahdi Army militia and a political bloc that is prominent in parliament and the government. His ties to Iran have also provoked concerns in some quarters.