Earlier in the day, a roadside bomb went off near a police patrol wounding four people, including three policemen, in southern Kirkuk, 250km north of Baghdad.
In the town of Udhaim, 90km north of Baghdad, the bodies of two members of a government-backed Iraqi armed group were found dead after being kidnapped overnight by armed men wearing military uniforms.
Police said two other people kidnapped overnight were still missing.
Several other members of the armed group, known as the Awakening Council, or Sahwa, were killed earlier in the week.
The targeted killings of policemen, soldiers, government officials and former fighters are stoking tensions in Iraq following a parliamentary election in March that produced no clear winner and has yet to yield a government.
The killings are the latest blow in what appeared to be a campaign to undermine Iraq's fragile security gains.
Iraqi leaders promised to give government jobs to some 90,000 Sahwa members, but only about 42,000 of the fighters have been offered jobs, according to government officials.
Thousands of other Sahwa fighters were asked to stay with their neighbourhood security patrols through Iraq's March 7 parliamentary election and until a new government is formed.
The Awakening Councils were credited with helping to significantly cut violence since the worst of the sectarian bloodshed in 2006-07, when tens of thousands of people were killed.
Before joining the fight against al-Qaeda in Iraq, members of the Awakening Councils were accused of killing US and Iraqi soldiers.
Some of their former leaders and fighters were arrested by Iraqi security forces to face those accusations, forcing others into hiding.
Many other Sahwa leaders have been targeted by bombings and assassinations in recent weeks in what appear to be either acts of revenge or part of a campaign to scare them back into the ranks of the uprising.