Two other US service members were injured and are receiving medical treatment, the statement said.
The forces were not in contact with enemy forces at the time, according to the statement.
"We are deeply saddened by the loss of one of our own," said Army Gen. John Nicholson, commander of US Forces-Afghanistan. "Our deepest sympathies and prayers are with the families and friends of our fallen and injured comrades."
The incident brings the total number of US forces killed this year in Afghanistan to 14.