A US servicemember was killed and four were wounded on Monday in combat in eastern Nangarhar province, military officials said.
General John Nicholson, commander of US Forces Afghanistan (USFOR-A), paid tribute to the fallen soldier on Twitter, writing: "We are deeply saddened by the loss of one of our own".
"At this very hard time our heartfelt sympathies go out to the families and friends of our fallen and wounded brothers", Nicholson added.
Sen. Cory Booker, D-N.J., said in a statement that the service member killed is Army Sergeant First Class Mihail Golin of Fort Lee, N.J. He says Golin "served our nation with courage and distinction, and his death is a loss that will be felt across New Jersey".
Fighting has been particularly fierce in the Nangarhar province, where several service members were killed previous year.
Gresback said USA and Afghan forces are making "significant progress" in the area, and predicted a long winter for militants in the region.
Troops based in Afghanistan have been aiding the nation's security forces in engaging ISIS-tied groups and the Taliban since forcing ceasing combat operations almost four years ago.
One US soldier was killed and 4 more were wounded on New Year's Day in Afghanistan.
President Trump said in August he'd up the number of airstrike, while no longer announcing the number of troops stationed in Afghanistan.
The slain servicemember, the first US combat fatality this year, was not identified.