The assailants in the mainly Shi`ite town of Balad, 80 km (50 miles) north of Baghdad, sprayed machine gun fire from their cars for around 10 minutes before speeding off.
The area, which was nearly overrun by Islamic State militants in 2014 and remains around 40 km from a frontline held by Shi`ite militiamen, is heavily secured.
The attackers passed three police checkpoints before reaching their target, said police sources who declined to be identified as they were not authorized to speak to the media.
Iraqi authorities have come under heightened criticism over security breaches that allowed suicide attackers to set off three bombs on Wednesday in Baghdad, killing at least 80 people in the bloodiest day in the capital so far this year.
The country is also facing a political crisis over a cabinet overhaul that has crippled government for weeks and threatens to undermine the U.S.-backed war against Islamic State, which still controls swathes of territory in the north and west which it seized in 2014.
Shooting in northern Iraqi town kills 12 - police, hospital sources
13 May 2016
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Three gunmen opened fire overnight on a cafe in northern Iraq where young men had gathered at the start of the weekend holiday, killing at least 12 and wounding 25, police and hospital sources said on Friday.
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