A wave of car bombs in southern Iraq has killed 30 people as the country grapples with a spike in violence and prolonged political deadlock, sparking fears of a sectarian war.

A total of seven vehicles rigged with explosives went off on Sunday in five cities south of Baghdad, the capital, during morning rush hour, leaving 56 people wounded in primarily Shia Muslim areas of Iraq.

No group immediately claimed responsibility for the attacks, but Sunni groups linked to al-Qaeda frequently target Shias, whom they regard as apostates, in coordinated attacks.

Car bombs went off in Kut, Aziziyah, Mahmudiyah, Nasiriyah and Basra, officials said.

In Kut, the provincial capital of Wasit located 160km south of Baghdad, a car bomb exploded outside a restaurant in an industrial area packed with vehicle repair garages, killing seven people and wounding 15.

Another car bomb in nearby Aziziyah, in the town's main marketplace and near a Shia mosque, killed five and wounded 10.

Twin blasts in the southern port city of Basra, meanwhile, killed five people, including a bomb disposal expert looking to defuse one of the rigged vehicles.

At least three others were killed in bombings in Nasiriyah and Mahmudiyah.

The violence was the latest in a sharp rise in attacks nationwide, with last month registering the highest death toll since 2008, sparking fears of a return to the all-out sectarian war that blighted Iraq in 2006 and 2007.

There has been a heightened level of unrest since the beginning of the year, coinciding with rising discontent among the Sunni Arab minority that erupted into protests in late December.

Analysts say a lack of effort by the Shia-led authorities to address the underlying causes of the demonstrations has given armed groups fuel and room to manoeuvre to carry out their activities.

The outgoing UN envoy to Iraq Martin Kobler has warned the violence is "ready to explode".