Sunday's attack in the town of Bargh-e-Matal in Nuristan province also wounded some other troops, said Lt. Cmdr. Christine Sidenstricker. She did not have an exact number of wounded.
Sidenstricker did not provide more details on the attack, saying only that it was not a roadside bomb or suicide bomber.
The death brings to 105 the number of U.S. troops killed in Afghanistan so far this year, compared with 151 U.S. deaths in all of 2008. Overall, 194 international troops have died in Afghanistan this year, according to an Associated Press count based on official announcements.
Elsewhere in the east, a roadside bomb killed a district police chief and his three bodyguards Monday in Wardak province, said Shahidullah Shahid, a spokesman for the governor.
On Sunday, the military reported the deaths of two U.S. Marines in Afghanistan's dangerous south, where thousands of American troops have deployed in a massive operation to oust Taliban fighters from the country's opium poppy region.
The two Marines were killed Saturday in Helmand, but military officials did not release any other details nor give a specific location.
Some 4,000 Marines moved into Helmand province this month, the largest Marine operation in Afghanistan since the 2001 U.S. invasion. They have met little head-on resistance but remain vulnerable to guerrilla tactics like suicide and roadside bombs.