Three other soldiers were wounded in the attack, the military said in a statement.
The soldiers were on a combat patrol Tuesday when they were struck by an explosively formed penetrator, or EFP, the military said in a statement. They had been returning to a U.S. military base after conducting an escort mission, it said.
EFPs fire a slug of molten metal capable of penetrating even the most heavily armored vehicles, and are have been responsible for hundreds of U.S. deaths in Iraq.
The victims' names were withheld pending family notification.
At least 3,874 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.