Iraqi officials say several car bombs have exploded in the volatile northern city of Mosul, killing at least 11 and wounding dozens.

The Monday evening blasts follow a string of bombings earlier in the day that killed a total of 25 others, extending a spike in violence that is raising fears Iraq is spiraling into a new round of sectarian violence.

Police in Mosul said a suicide bomber rammed his car into a police post, killing seven police and one civilian. In another attack, a bomber detonated his vehicle at a security checkpoint, killing three. Officials were unable to provide casualty tolls for the other Mosul attacks.

Hospital officials confirmed the death tolls. All officials spoke on condition of anonymity because they weren't authorized to release the details to reporters.

There was no immediate claim of responsibility for the attacks -- as has been the case for much of the violence in recent weeks -- but coordinated car bombings in civilian areas are frequently the work of al Qaeda's front group in Iraq, known as the Islamic State of Iraq.

According to the United Nations, at least 1,045 Iraqi civilians and security personnel were killed in May. The tally surpassed April's 712 killed.