The British prime minister is in the Afghan capital, Kabul, for talks with Afghan President Hamid Karzai.
GordonBrown arrived in Afghanistan Saturday on a previously unannouncedvisit. He met with British troops in southern Helmand province beforetraveling to the capital.
British military officials say it is the closest the British prime minister has ever gotten to the front lines in Afghanistan.
Hisvisit comes just one day after four British soldiers were killed inHelmand - one by a roadside bomb and three by a 13-year-old suicidebomber.
Mr. Brown denounced the Taliban for using such tactics.
Theprime minister released a statement calling the soldiers' deaths a"tragic loss" and saying fighting the Taliban puts British forces inthe front line against terrorism.
In a separate development,U.S. and Afghan forces say they killed six suspected militants anddetained 16 others in operations in southern Afghanistan Thursday andFriday.
Elsewhere in the country's south, NATO said its troopsfired on a speeding bus that failed to heed warning shots on Friday,killing at least three civilians on board.
The alliance says aNATO foot patrol fired the warning shots as the bus veered toward thetroops on the highway that links Kabul to Kandahar.
Civilian deaths at the hands of international troops have caused tension between the Afghan government and Western governments.
Mr.Karzai has repeatedly called on international forces to do all they canto prevent civilian casualties during military operations.