A dozen car bombs and suicide blasts in Shi'ite Muslim districts across Baghdad and south of the Iraqi capital have killed more than 50 people on the 10th anniversary of the US led invasion.
Sunni Islamist insurgents linked to al Qaeda are regaining ground in Iraq and have stepped up attacks on Shi'ite targets, Reuters reports.
One car bomb exploded in a busy Baghdad market on Tuesday, three detonated in the Shi'ite district of Sadr City and another near the entrance of the heavily fortified Green Zone.
A suicide bomber in a truck attacked a police base in a Shi'ite town south of the capital, officials said.
A decade after US and Western troops toppled Saddam Hussein, Iraq still struggles with insurgents, sectarian friction and political feuds among Shi'ite, Sunni and Kurdish factions who share power in the government.
In a sign of concern over security, the government has postponed local elections in two provinces, Anbar and Nineveh, for up to six months because of threats to electoral workers and violence.
No group claimed responsibility for the Baghdad blasts, but Islamic State of Iraq, a wing of al Qaeda, has vowed to take back ground lost in its war with US troops. This year the group has carried out a string of high-profile attacks.
Violence is still below its peak when tens of thousands were killed after Sunni Islamists bombed the Shi'ite Al Askari shrine in 2006, provoking a wave of retaliation by Shi'ite militias.
But security officials say al Qaeda's local wing is regrouping in the desert of Anbar province bordering Syria and suicide bombers have carried out attacks nearly twice a week since January, a rate not seen for several years in Iraq.
Further complicating security, thousands of Sunni protesters are also rallying in Anbar against Prime Minister Nouri al-Maliki, whose Shi'ite-led government they accuse of marginalising their minority sect since the fall of Sunni strongman Saddam.
Syria's war next door is also whipping up Iraq's volatile mix. Iraq is exposed to a regional tussle for influence between Turkey, which backs Sunni rebels fighting President Bashar al-Assad, and Shi'ite Iran, the Syrian leader's main ally.