BAGHDAD — A suicide bomber detonated an oil tanker rigged with explosives at a police station north of Baghdad on Wednesday, killing seven policemen, while attacks elsewhere left at least eight dead, officials said.

Iraq is mired in its worst violence since 2008, with more than 5,500 people killed this year despite major military operations targeting insurgents and tightened security measures.

In Wednesday's deadliest attack, a suicide bomber drove an explosives-rigged tanker in front of police station in Muqdadiyah, in restive Diyala province, and detonated it at the entrance, police and a doctor said.

The attack killed seven people and wounded 11 others, all police, and caused massive damage to the station.

The bombing is the latest in a string of attacks targeting police in the past week in Kirkuk, Salaheddin and Diyala provinces.

Elsewhere in Iraq, attacks on police killed three others.

In Salaheddin province, north of Baghdad, a roadside bomb targeting a police patrol killed a policeman and wounded two others, while a gun attack left a policeman dead in the province's north.

In Baghdad, a policeman was shot dead while on patrol in the Shiite slum neighborhood of Sadr City, while two roadside bombs in the capital left three others dead, including an anti-al-Qaida militiaman.

From late 2006 onwards, Sunni tribal militias, known as the Sahwa, turned against their co-religionists in al-Qaida and sided with the U.S. military, helping to turn the tide of Iraq's bloody insurgency.

But Sunni militants view them as traitors and frequently target them. The government has increasingly turned to Sahwa fighters as it combats a surge in unrest.

Meanwhile, in the northern city of Mosul, two separate shootings killed two civilians, officials said.

The level of violence in the country rose sharply after security forces stormed a Sunni protest camp in northern Iraq in April, sparking clashes in which dozens died.

Authorities have made some concessions aimed at placating the protesters and the Sunni minority in general, such as freeing prisoners and raising the salaries of the Sahwa.

But Sunnis insist they are still marginalized by the Shiite-led government and unfairly targeted by security forces.