The explosion occurred in Kandahar province, the spiritual birthplace of the Taliban. No other information, including the victims' names or which branch of the military they served in, was released.
U.S. military officials have said they expect a 50 percent rise in the number of roadside or suicide bomb attacks this year. At least 76 U.S. troops have died in Afghanistan so far in 2009, a record pace.
Elsewhere in the Afghan south, international and Afghan forces killed 16 Taliban militants in a gunbattle, police said Friday. One police officer also died in the fighting, they said.
NATO forces confirmed there was a clash in Uruzgan province on Thursday, but spokesman Lt. Cmdr. Christopher Hall said they only had reports of five dead, all of them militants.
