Hours before the Kirkuk attack, Sunni cleric Salah al-Nuaimi urged calm among Iraqis during a joint Sunni-Shiite sermon Friday in Baghdad aimed at easing sectarian tensions.
"Enough is enough," al-Nuaimi told worshippers at a Baghdad mosque. "We all love Iraq, we are all Iraqis and we want to be united. We want to stop the bloodletting, and develop and build Iraq."
Earlier in the day, a suicide car bomber struck a police patrol outside the northern city of Mosul, killing four policemen, a police officer and a medical official said. Mosul is 360 kilometers (225 miles) northwest of the Iraqi capital.
And outside the northern city of Tikrit, 130 kilometers (80 miles) north of Baghdad, drive-by shooters armed with pistols fitted with silencers killed a senior police officer. The attack took place in the town Shirqat, a police officer said.
Officials also provided details of new attacks on Iraqi Shiites late the previous night.
In one of the attacks on Shiites, a suicide bomber rammed his explosives-laden motorcycle into a funeral tent for a Shiite family in the town of in Muqdadiyah, about 90 kilometers (60 miles) north of Baghdad, officials said. The late Thursday evening explosion killed 13 people and wounded 24, the officials said.
In the northern town of Dujail, about 80 kilometers (50 miles) from Baghdad, a parked car bomb went off outside a Shiite mosque late on Thursday. As people gathered around the blast site, another bomb went off. That twin bombing killed at least 11 people and wounded 25, mayor Nayif al-Khazrachi said. Two medical officials, who weren't authorized to speak publicly, confirmed the casualty figures.
The two attacks raised the overall death toll Thursday from a series of attacks, which included assaults on police stations in the cities of Ramadi and Fallujah west of Baghdad, to 40.
On Wednesday, gunmen launched an assault on an army checkpoint and special oil industry police assigned to protect a nearby pipeline in the western Iraqi desert, killing at least 14 troops there.