A suicide car bombing has killed 13 people at a police station in the Iraqi city of Kirkuk, reports say.
The car that struck was reportedly packed with nails and TNT
The BBC's Stephen Sackur at the scene says a car exploded in a ball of fire in a Kurdish neighbourhood.
The blast, which wounded more than 50 people, is at least the fourth this year to target Iraqi security services.
US Defence Secretary Donald Rumsfeld arrived in Baghdad on a previously unannounced visit on Monday, shortly after the blast took place.
It is the fourth trip Mr Rumsfeld has made to Iraq since Saddam Hussein was toppled nearly a year ago.
He was met by Paul Bremer, the US administrator in Iraq, and taken to a briefing by General Martin Dempsey, who commands the US First Armoured Division.
Mr Rumsfeld is reported to be assessing plans for a reduction of US troops, in Baghdad and in the country as a whole.
Rumsfeld arrived unannounced in Baghdad to assess plans for Iraq
His visit came as United Nations Secretary General Kofi Annan said in a report to the UN Security Council that elections could be held in Iraq by the end of 2004.
However, he said there were still concerns about security and there needed to be consensus on a framework for the elections, including which electoral system would be used and what type of voter registration would be employed.
The problem of attempting to hand back control of security matters to Iraqis was underlined by the massive blast in Kirkuk on Monday morning.
The bombing in Kirkuk took place at about 0800 (0500 GMT), as one shift was replacing another and the station was full of people.
An Oldsmobile car packed with nails and 50kg of TNT drove into the unprotected building, the police station chief Colonel Adel Zain al-Abadin told AFP news agency.
The powerful bomb scattered body parts, and pools of blood stained patches of snow on the ground.
About 40 people were injured, many seriously, said a doctor at the local hospital.
Ten people died, including at least one bomber. One report has suggested there were two.
Our correspondent Stephen Sackur says the attack in Kirkuk was clearly aimed at Iraqi police. There were no Americans present when the bomb exploded, he says.
Iraqi insurgents accuse Iraqi police officers of collaborating with the US-led occupation, analysts say.
POLICE STATION ATTACKS
23 February 2004: Car bomb in Kirkuk kills 13 people, injures more than 50
14 February: At least 20 killed in gun battle outside Falluja station
10 February: At least 45 die in blast in Iskandariya
31 January: Nine killed in blast outside Mosul station
14 December 2003: Car bomb in Khalidiya kills 17
22 November: At least 18 die in twin bombings in Baquba and Khan Bani Saad
More than 300 officers have been killed since the new police force was established after the fall of Saddam Hussein's regime.
Kirkuk is Iraq's fourth-largest city and lies in the heartland of the country's northern oil fields.
It population is a volatile mix of Arabs, Kurds and Turkmen.
More than 100 people were killed in a double suicide bombing of Kurdish political party buildings in the city of Irbil on 1 February.