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, 180 miles north of Baghdad.
The bomber detonated his 1990 car as police were changing shifts at Rahimawa station, according to the station's chief, Colonel Adel Ibrahim.
Colonel Thamer Abdul-Masih said the bomber's car followed policemen driving to the station in a Kurdish neighborhood and "ran into the last car in the convoy and exploded." US command in Baghdad said Iraqi police fired on the car but were unable to stop it.
Police Chief Torhan Yousef said seven policemen and the bomber were killed and 52 people were wounded. The US military said 35 people were wounded.
The blast devastated nearby buildings and injured civilians in a passing bus.
"I fell on the floor of the bus," said Awen Aras, 11, 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."
More than 300 people -- mostly Iraqis -- have been killed in suicide bombings against Iraqi security forces this year. Just this month, suicide bombers have struck Kurdish political offices in Erbil, a police station in Iskandariyah, an army recruiting station in Baghdad and a Polish-run military garrison in Hillah.
The United States intends to transfer power to the Iraqis on June 30, but its plans have caused controversies on several fronts. Leaders of the country's Shi'ite Muslim majority, long repressed under deposed dictator Saddam Hussein, demand quick elections to establish a government.
The United Nations backed the US stance that elections are impossible by June 30 but said yesterday that a vote could be held by January 2005 if planning begins at once. The report by UN envoy Lakhdar Brahimi also said tensions between Sunni and Shi'ite Muslims were "becoming entrenched and intercommunal politics more polarized."
Bremer welcomed the UN report, calling it a "constructive contribution."