Attacks in Iraq on Thursday killed at least 17 people, including 10 in a bomb at the home of two brothers in the police force, while officials warned Al-Qaeda was targeting ex-fighters who switched sides.

The bloodshed comes after a spate of attacks since US forces completed their withdrawal in December, with Iraq mired in a political standoff that has pitted the Shiite-led government against the main Sunni-backed political bloc.

In the deadliest attack, a bomb exploded at the home of policemen Ahmed and Jihad Zuwaiyin as they and their families were sleeping at 4:00 am (0100 GMT) in Mussayib, 60 kilometres (35 miles) south of Baghdad.

The blast killed the two, their wives and six children, said a police officer in Babil provincial capital Hilla and a doctor at Mussayib hospital, both on condition of anonymity.

The blast was caused by several roadside-type bombs placed near the house's outer walls, which destroyed it. Four people were wounded and six nearby houses also damaged.

Mussayib, a predominantly Shiite town, lies in a confessionally mixed region dubbed the Triangle of Death because of the frequency of attacks during the worst of the insurgency that followed the US-led invasion of 2003.

In the northern city of Kirkuk, meanwhile, three people were killed and five others wounded by a bomb on a motorcycle parked near a primary school in the city centre, police Brigadier General Adil Zain al-Abidine said.

Kirkuk is at the centre of a tract of disputed territory that is claimed by both the central government in Baghdad and authorities in Iraq's autonomous northern Kurdish region.

Gunmen targeting a real estate agents in Yarmuk, west Baghdad, killed at least three people, though there were differing accounts of the attack itself.

A medic at Yarmuk hospital said the attackers burst into a real estate agency and killed three, while an interior ministry official said four people, including two real estate agents, died when gunmen opened fire on their car.

A separate bomb attack at a billiards cafe in Saidiyah, south Baghdad, left at least 17 people wounded, the officials said.

And in the mostly 0Sunni town of Heet, 160 kilometres (100 miles) west of Baghdad, Imam Qatada Mansur al-Heeti was killed by a magnetic "sticky bomb" attached to his car after he left the mosque following evening prayers, a police colonel in the town said.

Heeti was known for his sermons against Al-Qaeda.

The interior ministry, meanwhile, warned that Al-Qaeda's front group in the country, the Islamic State of Iraq (ISI), was targeting its former members who have switched sides in a bid to cause a split between them and the government.

"Al-Qaeda is putting pressure on members of the Sahwa to force them to abandon their national position," the deputy interior minister, Adnan al-Assadi, said in a statement posted on the ministry website.

The Sahwa is a tribal militia force comprised of Sunni Arabs who sided with US forces from late 2006 onwards, helping turn the tide of Iraq's insurgency.

Assadi's remarks came just days after assassins killed Mullah Nadhim al-Juburi, an ISI leader-turned-critic who had been working with Iraq's national reconciliation commission.

Reflecting ongoing sectarian tensions amid a political row in Iraq, messages were posted on Monday on the Honein jihadist forum vowing further attacks targeting Iraqi Shiites.

"The lions of the Islamic State of Iraq (will not cease their operations)... as long as the Safavid government continues its war. We will spill rivers of their blood as reciprocity," ISI said in a statement claiming responsibility for attacks on Shiite pilgrims in the past month.

The jihadists often invoke Iran's Safavid past, referring to the Shiite dynasty that ruled Persia between the 16th and 18th centuries and conquered part of Iraq, when denouncing the Baghdad government, which they say is controlled by Iran.