A suicide bomber killed a policeman who had stopped him at the entrance to a police station in the Pakistani capital of Islamabad on Monday.
Police say the Special Branch operated from the station in the Sitara Market neighbourhood of the capital where the bomb went off.
Taliban militants and jihadi groups linked to al Qaeda have run a campaign of violence to try to destabilise Pakistan.
A suicide truck bomb attack on the Marriott hotel in Islamabad last September and the assault by gunmen on the Sri Lankan cricket team in Lahore this month were measures of the growing danger.
Pakistani President Asif Ali Zardari called on Britain and the United States earlier on Monday to do more to help his government fight terrorism.