No one immediately claimed responsibility for the attack, which bore the hallmarks of the extremist Islamic State group. Since late last year, the group has suffered a string of territorial losses, most recently in Fallujah, where it was driven out last month by Iraqi forces after occupying the city for more than two years.
But the extremists have continued to carry out near-daily bombings in and around Baghdad, as well as complex attacks in other countries.
Eight policemen and six civilians were killed and up to 41 people were wounded, the officers said, adding that the explosion also damaged nearly 20 cars lined up at the checkpoint.
A medical official confirmed the casualty figures. Both officials spoke on condition of anonymity as they were not authorised to talk to the media.
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Yesterday, IS claimed responsibility for a suicide attack on a checkpoint in Baghdad that also killed 14 people and wounded 31.
The Sunni militant group recently stepped up its attacks far from the front lines in what Iraqi officials see as an attempt to distract from their battlefield losses.