The bombing occurred as Defense Secretary Donald H. Rumsfeld visited Baghdad to look at the state of readiness of Iraq's embattled security forces, which have born the brunt of the suicide strikes.
U.S. administrator L. Paul Bremer told reporters after meeting with Rumsfeld that Iraq has seen "a real step up" by "professional terrorists from al Qaeda and Ansar al-Islam in conducting suicide attacks."
Kirkuk has also seen rising ethnic tensions as Kurds, Arabs and Turkomen compete for control of the city, located in one of the world's richest oil-producing regions, 300 kilometers (180 miles) north of Baghdad.
In other recent developments:
The bomber detonated his white 1990 Oldsmobile just as police were changing shifts, and a group of 20 policemen were gathered outside the Rahimawa station in a Kurdish neighborhood of the city, the station's chief, Col. Adel Ibrahim, said.
Col. Thamer Abdul-Masih, chief of the Facilities Protection Service, said the bomber's car followed policemen driving to the station for duty and "ran into the last car in the convoy and exploded."
"Whoever did this had been watching and knew the procedure of the policemen's shifts," he said.
Police Chief Torhan Yousef said seven policemen were killed in addition to the bomber and 52 people were injured. The U.S. military said 35 people were injured. Among the dead was the station's deputy chief, Abdul-Masih said.
Blood was splattered over the station's entrance, and parts of the bomb-laden car, including the engine lay scattered in front. Abdul-Masih's office was littered with glass and torn curtains.
The injured, most of them Kurds but also Arabs and Turkomen, included a schoolboy and four girls from a nearby high school. The blast devastated nearby buildings, destroyed several cars and injured civilians in a passing bus.
"I fell on the floor of the bus," said Awen Aras, an 11-year old girl as she lay in a hospital bed, her leg in a cast. "Everything was flying around me after I heard a very loud explosion. There was a big fire and policemen carried me off the bus and took me to the hospital."
In Baghdad, Rumsfeld was told that vehicle bombings have supplanted insurgent attacks as the major threat to coalition forces. Brig. Gen. Mark Kimmitt, coalition deputy operations chief, said attacks on U.S. and allied forces have dropped from 50 per day in November to between 15 and 20 a day and gun battles with guerrillas have been supplanted by remotely detonated bombs and suicide bombers.
More than 300 people — mostly Iraqis — have been killed in a string of vehicle and suicide bombings against Iraqi security forces this year. Suicide bombers have struck this month against Kurdish political offices in Irbil, a police station in Iskandariyah, an army recruiting station in Baghdad, and a Polish-run military garrison in Hillah.
Rumsfeld praised Iraqi police and civil defense forces for their resolve in confronting the threat.
"We're looking forward to seeing Iraqis take over the responsibility for the security of your country," he told members of the Iraqi Civil Defense Corps.
The United States intends to transfer power to the Iraqis on June 30 — but its plans have hit controversies on several fronts. Leaders of the country's Shiite Muslim majority demand quick elections to establish a government, and an influential cleric on Monday warned of civil war between Iraq's ethnic groups if a vote is delayed.
A senior Iraqi cleric warned Monday that delaying national elections would be a "timebomb that could explode at any minute."
"Without elections, our national institutions will remain shaken, unrecognized and distrusted by the people," Grand Ayatollah Mohammed Taqi al-Modaresi told reporters in the Shiite holy city of Karbala.
The uncertainty "makes us fear for the future of Iraq" and the possibility of "civil war," he said.
After decades of oppression by the country's Sunni minority under Saddam, Shiites are eager to translate their numerical superiority into votes, and fear that an appointed government might try to postpone elections indefinitely to keep itself in power.