Anti-war activists took to the streets before the fourth anniversary of the Iraq war.
Another soldier died the same day in a non-combat related incident, the military said.
The deaths raise to at least 3,215 the number of US troops who have died since the Iraq war started in March 2003, according to a count by the Associated Press news agency.
Armed groups also killed three people, including a policeman, in two separate incidents early on Sunday in Baghdad despite a massive security crackdown in the Iraqi capital.
Security officials said a policeman and a civilian were killed and five policemen wounded when a roadside bomb struck a police patrol near the renowned Al-Mustansiriyah University in east Baghdad.
Another civilian was killed and one wounded in a mortar attack in central Baghdad‘s Al-Fadhel district, another security official said.
Armed groups have managed to carry out attacks in Baghdad despite the presence of 90,000 US and Iraqi troops on the city’s streets as part of Operation Fardh al-Qanoon [Imposing Law] launched to curb the violence.