Six Iraqi policemen have been killed in a car bomb blast in Saddam Hussein's hometown of Tikrit, in northern Iraq, the US military says. Aljazeera reported the bomb exploded in front of Iraqi police headquarters in Tikrit city, which lies 175km north of Baghdad. "At approximately 9.30am (0630 GMT) on 11 January in northern Tikrit, anti-Iraqi forces detonated a vehicle-borne improvised explosive device in the vicinity of a police station, killing six Iraqi police," the US military said in a statement. Iraqi journalist Muhammad al-Badri told Aljazeera the booby-trapped car was parked at the side of the road leading to the police headquarters. There was a loud explosion that rocked the city and columns of smoke were rising from the explosion site. **Security tightened*** Al-Badri said security had been tightened as Iraqi police set up checkpoints at many roads, due to warnings of car bombs targeting police headquarters, the governorate building and security forces. The attack came a day after Baghdad's deputy police chief, Amir Nayif, was assassinated, in one of a string of deadly attacks against Iraqi security forces in the run-up to the planned 30 January elections. "As the Iraqi police continue to get stronger, and continue to pose a threat to the insurgents and terrorists, they will be targeted," said US military spokesman Major Neal O'Brien. British Prime Minister Tony Blair, the top US ally on Iraq, said on Sunday that the US and Britain would send a team to Iraq to reassess the security situation and to help build up the country's own security forces. **Ukraine Orders Pullout*** Ukraine's outgoing president Leonid Kuchma ordered officials yesterday to bring the country's 1,600 troops in Iraq back home within six months, after eight of its soldiers were killed in an explosion. He told his defence and foreign ministers to draw up the plans in an emergency meeting following Sunday's blast. **PHOTO CAPTION*** A tied up Iraqi detainee is guarded by US soldiers of the 1st Battalion, 22nd Infantry Regiment of the 4th Infantry Division during a raid in Tikrit. (AFP)