A suicide bomber rammed a car into a police station in the northern Iraqi city of Kirkuk on Monday, killing 13 people and wounding 51 others, a police official said.
The attack occurred shortly before US Defence Secretary Donald Rumsfeld flew into Baghdad on an unannounced visit to assess security in the troubled country.
Police Lieutenant Salam Zangana said all of those killed were policemen.
"He took us by surprise. We didn't even manage to fire a single bullet at the bomber," said policeman Saman Ali.
More than 300 Iraqi policemen have been killed since a US-led invasion toppled Iraqi leader Saddam Hussein in April.
A police official said the attack was carried out by a suicide bomber driving a car in a Kurdish section of Kirkuk.
"Parts of the suicide bomber, his legs and hands, were scattered inside the police station," said Amjad Reda, a slightly wounded policeman whose skin was blackened by the blast.
The explosion badly damaged 13 cars and sent car parts flying over 100 metres (yards) away.
The bomber struck when police were vulnerable while changing shifts and loading their weapons, a pattern seen in other bombings.
Pools of blood covered ice and snow patches after the bomber drove his car into the gate of the unfortified police station.
Armed only with AK-47 assault rifles, Iraqi police often complain that US troops do not provide them with protection.