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.
(AP, Reuters)