The deaths bring to 500 the number of American service members who have died since the Iraq war began.
Two Americans also were wounded in the attack, which occurred when a Bradley Fighting Vehicle struck an explosive device on a road near Taji, about 20 miles north of Baghdad, said Lt. Col. Bill McDonald, a spokesman for the 4th Infantry Division.
The vehicle caught fire, killing the three Americans and two Iraqis who were on joint U.S.-Iraqi patrol, McDonald said.
A U.S. quick reaction force rushed to the area and detained three men fleeing in a white truck, he added. Soldiers found bomb-making material in the vehicle, he added.
CNN reported that the Bradley flipped over and caught fire.
Also Saturday, the military said a U.S. soldier died from a non-hostile gunshot wound south of Baghdad. The incident occurred Friday evening near Diwaniyah south of Baghdad, the command said in a statement. No further details were released.
The deaths bring to 500 the number of U.S. service members who have died since the Iraq conflict began on March 20.