Afghan and U.S. troops were on a patrol when they came under small arms fire from enemy forces northeast of Kandahar, the military said in a statement. It said U.S. and Afghan soldiers returned fire, and aircraft and helicopters attacked the enemy positions.
A U.S. soldier and one Afghan National Army soldier were also wounded in the firefight, but were in stable condition at a nearby U.S. medical facility. One insurgent was killed, it said.
"This is a sad day for us all here in Afghanistan," said Brig. Gen. Jack Sterling Jr., deputy commanding general of Combined Joint Task Force-76.
The statement did not identify the killed and wounded soldiers.
On Monday, four coalition soldiers were wounded when their vehicle struck a mine in Kandahar province. They were also in stable condition.
A week earlier, a Canadian soldier in the U.S.-led coalition was slightly wounded in a blast that killed the attacker and a civilian. A suicide car bombing in Kandahar in November, apparently targeting Westerners, killed three Afghan civilians.