"We are deeply saddened by the loss of one of our own", said Army Gen. John W. Nicholson Jr., the senior USA military commander in Afghanistan.
The service member's name is not being immediately disclosed pending notification of next of kin. The two others have returned to duty.
During an unannounced visit to Afghanistan last month, Vice President Mike Pence said American forces would stand "shoulder to shoulder" with their Afghan counterparts as they fight the Taliban and other terror groups. "Our heartfelt sympathies go out to the families and friends of our fallen and wounded brothers".
Fighting has been particularly fierce in the Nangarhar province, where several service members were killed previous year.
Spokesperson for the 209th Shaheen Corps, Nasratullah Jamshidi, said that among the dead were two foreigners and several top IS commanders, including the second highest member of the group in northern Afghanistan, Qari Shujah. Militants in Achin were pushed into mountains that border Pakistan and were attempting to move west from there through access points in the mountains, the general said.