Eight car bombs different districts of the Iraqi capital, Baghdad, killed 20 people on Monday and 11 others were killed by attacks in the southern city of Basra, police and medics said.
Explosions were also reported in the city of Samarra but there was no immediate word on casualties.
Scores of people have been killed in attacks over the past week.
Two car bombs hit Basra, located 420km southeast of Baghdad.
The first bomb struck the Hananiya neighborhood, near a busy market and restaurants, and the second was detonated inside a bus terminal in Saad Square.
More than 700 people were killed in April by a UN count, the highest figure in almost five years.