A series of car bomb attacks killed at least 18 people in Baghdad and wounded 29 in a busy market area, police said.
The deadliest blast took place in the north of the Iraqi capital in the mainly Shia neighbourhood of Shula, where a car bombing killed at least eight people and wounded 14, an interior ministry official said.
Other bombings were reported in the Amriyah, Ghazaliyah and Yarmuk neighbourhoods, west of Baghdad, and in Dora, south of the capital, killing at least four people, AFP reported.
There is some confusion over the total number of wounded, with some reports saying at least 37 people were injured.
Sectarian-based violence in Iraq had decreased since its peak in 2006-2007, but suicide attacks have increased over the past year.
On 13 May, two bomb attacks targeted the country's security forces in Baghdad, leaving six dead.
According to official figures, a total of 126 Iraqis have been killed in violence since April.