At least 27 people have died in attacks targeting mainly Shi'ite Muslims across Iraq, intensifying fears of a return to full-blown sectarian war.
More than 1000 people were killed in militant attacks in Iraq in May, according to the United Nations, making it the deadliest month since the sectarian slaughter of 2006-07.
Two car bombs exploded separately in the predominantly Shi'ite southern city of Basra, 420 km southeast of Baghdad, killing at least five people and wounding 10, police said.
Car bombs also targeted Shi'ites in Najaf, Nassiriya, Kut, Hilla, Tuz Khurmato and Mahmudiya in southern Baghdad. Near the northern city of Mosul, gunmen shot dead six policemen at a checkpoint in Hadhar, police said.
Reuters reports no group claimed responsibility for the attacks but Sunni Islamist insurgents and al Qaeda's Iraqi wing have increased operations since the beginning of the year as part of a campaign to increase inter-communal tensions.
Sectarian relations have been further strained by the war in neighbouring Syria, where Sunni rebels are fighting to overthrow a leader backed by Shi'ite Iran. Sunni and Shi'ite Iraqis have been crossing into Syria to fight on opposing sides.