Clashes in northern Iraq killed nine police and four gunmen on Friday, while other attacks, including a car bomb near a Sunni mosque, left at least six more people dead, officials said.

Mortar rounds were fired at checkpoints in the fierce fighting that also left another seven police wounded, police and a doctor said.

In Rashidiyah, north of Baghdad, the car bomb exploded as worshippers left Friday prayers at Al-Ghufran mosque, killing at least five people and wounding 30, officials said.

A roadside bomb killed a police captain in Baiji, north of the capital.

And in Al-Amil in south Baghdad, a magnetic "sticky bomb" blast wounded a police captain, while a roadside explosion wounded three more police in Taji, north of the capital, sources said.

The violence came a day after the United Nations said April was the deadliest month for Iraq in almost five years.

A wave of unrest began on April 23 when security forces moved on Sunni anti-government protesters near the town of Hawijah in northern Iraq, sparking clashes that killed 53 people.

Dozens more died in the subsequent unrest, including in revenge attacks targeting security forces, raising fears of a return to the all-out sectarian conflict that claimed tens of thousands of lives from 2006 to 2008.

While violence has fallen from its peak during the sectarian conflict in 2006 and 2007, attacks are still common, and have killed more than 200 people each month so far this year.