A wave of attacks across Iraq, including twin car bombs in an ethnically mixed tinderbox city, killed 32 people Wednesday as a year-long surge of violence showed no signs of a let-up.

More than 100 people were also wounded in the violence, in and around Baghdad, as well as in Salaheddin, Kirkuk, Diyala and Babil provinces, all afflicted by regular bloodshed.

The attacks came a day after a suicide bomber killed a key anti-Qaeda leader battling militants in the conflict-hit province of Anbar.

In Wednesday's deadliest incident, two vehicles rigged with explosives went off in the centre of Kirkuk, killing eight people and wounding nine, said provincial health chief Sabah Mohammed.

Kirkuk, an oil-rich ethnically diverse city, lies at the centre of territory that Iraqi Kurdistan wants to incorporate into its three-province autonomous region over the objections of the central government in Baghdad.

No group immediately claimed responsibility for the attack, but Sunni militants frequently detonate bombs in the disputed territory, capitalising on poor communication between Kurdish and central government security forces.

Elsewhere in northern Iraq, a suicide truck bomb killed two people in Suleiman Bek, and two attacks in nearby Tuz Khurmatu, including a corpse booby-trapped with explosives, killed two others.

Both towns, like Kirkuk, lie in the disputed territory, which stretches from Iraq's border with Iran to its frontier with Syria.

Another car bomb, this one near the main hospital in Hilla, a Shiite-majority city south of Baghdad, killed seven people, security and medical officials said.

In and around Baghdad, four people were killed by a car bomb in a commercial area of a Sunni-majority neighbourhood, while six others died in shootings and bombings inside the capital and on its outskirts.

Elsewhere, in the restive provinces of Diyala and Salaheddin, both north of Baghdad, attacks left three dead.

Wednesday's violence came a day after a suicide bomber killed 11 people at a camp for families displaced from the conflict in the western desert province of Anbar, where security forces have struggled to retake territory from militants.

Among the casualties was Mohammed Khamis Abu Richa, nephew of a well-known anti-Qaeda militia leader, and himself a key tribal commander.

Though Abu Richa frequently criticised the government, he had fought militants opposed to the authorities, including the powerful Islamic State of Iraq and the Levant jihadist group, which he and Baghdad regarded as a common enemy.

Violence is running at its highest levels since 2006-2007 when Iraq was gripped by a brutal Sunni-Shiite sectarian war that killed tens of thousands.

More than 900 people were killed last month, according to figures separately compiled by the United Nations and the government.

More than 4,000 have been killed this year, according to an AFP tally.

Officials blame external factors for the rise in bloodshed, particularly the civil war in Syria, and insist that wide-ranging operations against militants are having an impact.

But the violence continues unabated, with analysts and diplomats saying the Shiite-led government needs to do more to reach out to the disaffected Sunni Arab minority to reduce support for militancy.