Officials say Iraqi security forces have killed three gunmen who attacked a checkpoint in the country's north amid escalating Sunni-Shiite tensions.

The officials say the police repelled the attack on Wednesday morning near the former al-Qaida stronghold of Mosul. The city is about 360 kilometers (225 miles) northwest of Baghdad.

A car bomb later struck a police patrol just north of Baghdad, killing a policeman and two civilians.

Medics in nearby hospitals confirmed the death toll. All officials spoke on condition of anonymity because they are not authorized to talk to the media.

On Tuesday, security forces stormed a Sunni protest camp in the northern town of Hawija, sparking deadly clashes. The unrest and a spate of other attacks, mostly targeting Sunni mosques, killed at least 56 people.