One U.S. service member died and two others were wounded during operations in southern Afghanistan on Tuesday, the Pentagon said.
The Department of Defense did not name the casualties, saying only that the incident took place near Marjah in Helmand Province.
"We are deeply saddened by this loss," U.S. Brig. Gen. Wilson Shoffner said in a statement.
American defense officials earlier told NBC News that U.S. Special Operations Forces were involved in a counter-terrorism operation in the Marjah area of Helmand province when they came under attack.
A U.S. medevac chopper called in to recover casualties then came under mortar and small-arms fire, the officials added. It was not clear if the helicopter had been hit by enemy fire or whether any casualties were sustained in that landing zone, the officials said, speaking on condition of anonymity.
U.S.-backed forces have been fighting to suppress the Taliban in Marjah for weeks. A spokesman for the Taliban — which frequently exaggerates its claims — said Tuesday the group had shot down a U.S. transport helicopter in Helmand.
In early December, insurgents launched a major offensive to take control of key districts in Helmand, a longstanding Taliban stronghold and the source of most of the opium that helps fund the movement.
Afghanistan has had a tense and violent start to the new year, as talks to revive the peace process loom next week. The winter in Afghanistan usually sees a lull in insurgent violence.
The Taliban claimed responsibility for a Monday car bomb attack on a compound for civilian contractors near the Kabul airport, hours after another suicide bomber blew himself up. And on Friday, a suicide bomber attacked a French restaurant popular with foreigners in Kabul, killing two people and injuring 18 others.