A car bomb exploded outside an air base used by U.S. forces near Dijiel, about 25 miles north of Baghdad, the U.S. military and police said.
One American soldier and two Iraqi civilians were wounded, said Army Sgt. Robert Powell, a spokesman for the 1st Infantry Division.
Powell said three suspects were detained near the site of the attack and taken to the base for questioning.
The injured soldier was in a stable condition after being evacuated to a military hospital, while the three Iraqis were treated at the scene, Powell said.
Witnesses said a Volkswagen exploded near the base, setting fire to an American Humvee.