Bomb attacks in Shi'ite areas of Baghdad and in northern Iraq killed more than 30 people on Wednesday, following weeks of violence by Sunni Islamist insurgents determined to spark sectarian confrontation.
Tensions between minority Sunni Muslims and the Shi'ites who now lead Iraq are at their highest since U.S. troops pulled out in 2011, with relations coming under more pressure by the day from the largely sectarian conflict in neighbouring Syria.
A string of car bombings hit Shi'ite neighbourhoods across the Iraqi capital Baghdad on Wednesday evening, including one outside a cafe, killing at least 18 people, police said.
Earlier, 10 people were killed when two car bombs exploded near government buildings in the ethnically mixed oil city of Kirkuk.
"There were two bodies on the ground outside the building, people were shouting and it was a mess everywhere," said Rawaa Rahman, a government employee in Kirkuk who was wounded in the hand.
A suicide bomber on a motorcycle also blew himself up near a police patrol in northern Baghdad, killing at least two officers, while a roadside bomb killed a policeman in a town near Mosul, 390 km (240 miles) to the north, police and medical sources said.
Relations between Iraq's Shi'ite, Sunni and ethnic Kurdish communities have come under growing strain since the last American troops left in December 2011.
The coalition government, split among Shi'ite, Sunni and Kurdish political blocs, is hobbled by disagreements about how to share power.
But the conflict in neighbouring Syria, where mostly Sunni rebels are trying to oust President Bashar al-Assad, has also put pressure on Iraq's delicate intercommunal balance.
Although violence is well below the height of sectarian slaughter in 2006-7, when tens of thousands were killed, Sunni Islamist insurgents now carry out attacks almost daily to try to undermine the Shi'ite-led government.
Al Qaeda's local wing, Islamic State of Iraq, and other Sunni insurgents are trying to use Syria's war to gain legitimacy and tap into frustrations among Iraqi Sunnis, hoping to regain ground they lost during their long battle with American troops.