The attack took place in the town of Bashmaya outside the city of Mosul, which has been one of the major flashpoints in a wave of bloodshed that has washed over the country since April and left more than 3,000 people dead.
The scale of the violence is intensifying fears of a return to the widespread sectarian killing that pushed the country to the brink of civil war after the 2003 US-led invasion.
A medical official confirmed the casualty figures. Both officials spoke on condition of anonymity because they are not allowed to talk to the media.
Insurgents this year have regularly attacked security forces in Mosul, a longtime militant stronghold.
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On Monday, a suicide bomber rammed his explosives-laden car into an army convoy, killing at least 13 people including 10 soldiers. Police found the bodies of four off-duty policemen yesterday on a road with bullet wounds in their heads. Gunmen in a speeding car also shot dead two other off-duty policemen as they were walking down a street.
And in Baghdad, police found three bullet-ridden corpses across the city, police and medical officials said on condition of anonymity as they were not authorized to brief media.
In the northern city of Tuz Khormato, about 200 kilometers north of Baghdad, a bomb hidden in a motorized cart exploded in a residential area, wounding 35 people and damaging several houses, police Col. Hussein Ali Rasheed said.
Overall levels of violence have since escalated and insurgent attacks have become more audacious, including raids this week against two high-security prisons near Baghdad that killed dozens and set free hundreds of inmates, including al-Qaida-linked militants.
Yesterday, al-Qaida's Iraqi branch claimed responsibility for the attack.