BAGHDAD: A wave of car bombs in southern Iraq killed 20 people on Sunday as the country grapples with a spike in violence and prolonged political deadlock, sparking fears of all-out sectarian war.

In all, seven vehicles rigged with explosives went off in five cities south of Baghdad during morning rush hour, leaving 56 people wounded in primarily Shiite Muslim areas of Iraq.

Car bombs went off in Kut, Aziziyah, Mahmudiyah, Nasiriyah and Basra, officials said. In Kut, provincial capital of Wasit and 160 kilometres (100 miles) 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 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.

Three others were killed in bombings in Nasiriyah and Mahmudiyah. The violence was the latest in a spike 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 authorities to address the underlying causes of the demonstrations has given militant 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".