A USA service member was killed Monday during combat in eastern Afghanistan, the Pentagon said.
Two of the injured soldiers are now receiving treatment at a local medical centre, and are said to be in a stable condition.
Four other service members were wounded during the combat engagement.
"At this very hard time our heartfelt sympathies go out to the families and friends of our fallen and wounded brothers", Nicholson added.
Additional information will be released as it is available.
Sen. Cory Booker says the Army had identified the dead soldier as Mihail Golin, of Fort Lee, New Jersey.
In late November, Nicholson said more US troops in Afghanistan would be sent to the front lines in 2018 and was frank about the fact it would place them in greater danger.
Navy Capt. Tom Gresback, a USA military spokesman in Kabul, said Tuesday that "there has been a tremendous amount of kinetic activity in the Achin district" of late, using a military term that typically connotes firefights and other violence. "We continue to apply increased military pressure on ISIS-K, forcing their movement from their front-line positions". As we have reported, "the recent commitment of about 3,000 additional troops will bring the total number of USA service members in Afghanistan to between 14,000 and 15,000", according to the special inspector general for Afghanistan reconstruction.
US support to the Afghan forces fighting ISIS-K is separate from its participation in the USA -led NATO Resolute Support mission, which turned 3 years old on Monday. The Washington Post reveals that eleven of those fatalities occurred during combat with seven taking place in the Nangahar province. He was a member of the 19th Special Forces Group. "They go through the passes of southern Nangahar and they move back to their home agency".
According to Nicholson, there are only about 1,000 ISIS fighters left in Afghanistan, with between 600 and 800 of them in Nangahar province.