BAGHDAD — Twelve people, among them six policemen, were killed and 14 others wounded in a series of attacks across Iraq on Wednesday, security and hospital officials said.

Six policemen were killed when a suicide bomber detonated a vehicle packed with explosives Wednesday night at a police checkpoint in Ramadi, 100 kilometres (60 miles) west of Baghdad, an officer said, adding that there were also an unspecified number of wounded.

In the restive northern city of Mosul, unidentified gunmen shot a man dead near his home, a police officer said, while two women were wounded in a roadside bomb attack.

Five people were also killed in a string of attacks in the central province of Diyala.

Four people were killed and seven wounded when insurgents detonated bombs at the homes of three town criers whose job was to awaken people for the Ramadan pre-dawn meal, at around 3:00 am (0000 GMT) in the town of Al-Hudaid, according to an Iraqi army colonel in Diyala's security command centre.

"Among the dead were a woman and a child, and two women and a child were among the wounded," the colonel said, speaking on condition of anonymity. He added that rescue workers were still searching the rubble of the houses, and warned the toll could rise.

Firas al-Dulaimi, a doctor at the main hospital in Diyala provincial capital Baquba, confirmed that four people had died and seven were injured.

None of the three town criers were among the casualties, the army colonel said.

In the centre of Baquba, meanwhile, an anti-Qaeda militiaman was gunned down at around 8:00 am (0500 GMT) by insurgents equipped with silenced pistols, according to the colonel.

The militiaman was a member of the Sahwa, made up of Sunni tribes that sided with the US military against Al-Qaeda from late 2006, helping to turn the tide of Iraq's bloody insurgency.

Also in Baquba, a roadside bomb targeting police Lieutenant Colonel Hamid al-Karkhi left the officer and his driver wounded, the army colonel said.

Meanwhile, in Baghdad, three people were wounded Wednesday morning when a roadside bomb struck against an Iraqi army patrol in Allawi, in the west of the capital, an interior ministry official said.

Wednesday's violence comes after Al-Qaeda's front group in Iraq threatened a campaign of 100 attacks, starting mid-August, to avenge the death of Osama bin Laden in a US special forces raid in Pakistan nearly four months ago.

Violence is down across Iraq from its peak in 2006 and 2007, but attacks remain common. A total of 259 people were killed in violence in Iraq in July, according to official figures, the second-highest figure in 2011.