They said a suicide car bombing followed by a car bomb struck near a police checkpoint in a crowded area of eastern Baghdad, also wounding at least 31 people.
Militants led by the Islamic State (IS) jihadist group overran swathes of Iraq in June, and security forces, Shiite militias and Kurdish fighters have been battling to regain ground.
The US began an air campaign against IS in Iraq on August 8, mainly in support of Kurdish forces in the north, though American warplanes have also carried out limited strikes in Salaheddin and Anbar provinces.