Two roadside bombs that exploded in Amriyah in western Baghdad, a car bomb in the northern district of Adhamiyah -- both of which are Sunni-majority -- and another vehicle in the Saidiyah neighbourhood also wounded at least 30 people, the sources said.
The car bomb in Adhamiyah, which struck near the massive Abu Hanifa mosque, killed at least seven people and wounded 22, while the twin bombings in Amriyah left four others dead.
The blasts came just ahead of the weekend in Baghdad, when markets and cafes are typically packed, and continue a trend of post-sunset attacks in the capital.
Violence in the city had previously been concentrated during morning rush hour.
No group immediately claimed responsibility for the attacks.
Sunni militant groups such as the powerful Islamic State of Iraq and the Levant jihadist group are often blamed for such bombings targeting civilians, including those against Sunnis, because the insurgent groups do not regard them as sufficiently faithful.
Elsewhere in Iraq, attacks north of the capital killed three people including a police colonel.
The bloodshed has been driven principally by anger among the Sunni Arab minority, who complain of mistreatment by the Shiite-led government and security forces, as well as by the civil war in neighbouring Syria.
More than 450 people have been killed so far this month and upwards of 2,100 since the beginning of the year, according to AFP figures based on reports from security and medical sources.
Analysts and diplomats have called for the Shiite-led authorities to do more to reach out to the disaffected Sunni minority in a bid to reduce support for militancy.