A wave of car bombs and shootings, mostly targeting Shiites, killed 28 people on Sunday as Iraq grapples with a spike in violence and prolonged political deadlock, sparking fears of all-out sectarian war.

At least 10 vehicles rigged with explosives went off in eight cities in Iraq's Shiite Muslim-majority south during morning rush hour, also leaving more than 100 people wounded, while the main northern city of Mosul witnessed a deadly shooting.

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

Car bombs exploded in Kut, Aziziyah, Nasiriyah, Basra, Mahmudiyah, Madain, Jbela and Najaf, 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 Shiite mosque killed five and wounded 10.

"The cafe and the street outside is covered in blood," said Hisham Shadhan, whose father owns a cafe badly hit in the Aziziyah attack.

"The car was parked just next to the cafe and when it went off, it destroyed the front part of the cafe. Many cars have caught fire, and it also caused huge damage to nearby shops."

The force of the blast overturned cars and left shrapnel strewn across the scene, but authorities quickly cleaned up much of the visible damage, an AFP journalist said.

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

Six others were killed and dozens more wounded in bombings in Nasiriyah, Mahmudiyah, Najaf, Madain and Jbela.

Early Sunday, three policemen were shot dead near the main northern city of Mosul, which is primarily Sunni Arab.

And also in north Iraq, two people were killed by a roadside bomb in the ethnically mixed town of Tuz Khurmatu, which lies in a tract of disputed territory claimed by both the central government and the autonomous Kurdish region.

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 Shiite-led authorities to address the underlying causes of the demonstrations has given militant groups fuel and room to manoeuvre to carry out their activities.

Political leaders have pledged to resolve a multitude of long-standing disputes and Prime Minister Nuri al-Maliki has met his two chief rivals, the Sunni parliament speaker and the Kurdish regional president, in a bid to ease tensions, but no tangible moves have been agreed.

Analysts and diplomats have voiced fears that the stalemate could persist until parliamentary elections next year.

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