A US service member was killed and four US troops were wounded during a "combat engagement" in Afghanistan on New Year's Day, the Pentagon has said.
The soldier died in Achin, Nangarhar province, along the Pakistan border - an area which has become a stronghold for the so-called Islamic State (IS).
The Pentagon did not release additional details or identify the US soldier who was killed.
"We are deeply saddened by the loss of one of our own," an official said.
"At this very difficult time our heartfelt sympathies go out to the families and friends of our fallen and wounded brothers," said Army Gen John Nicholson, commander of US forces in Afghanistan.
At least 15 Americans died in Afghanistan in 2017, according to icasulties.org, which tracks US deaths in foreign conflicts.
The Pentagon, which did not describe how the death occurred, said that two of the wounded soldiers are still recovering "in a nearby medical treatment facility and are in stable condition".
The other two injured soldiers have been returned to active duty, the statement said.
There are currently around 14,000 US soldiers stationed in Afghanistan.
At a November briefing, Gen Nicholson said that insurgents in that region are known to seek refuge in Pakistan after carrying out attacks in neighbouring Afghanistan.
"Remember most of these Daesh fighters came from Pakistan," Mr Nicholson said, referring to the IS terror group.
"They go through the passes of southern Nangahar and they move back to their home agency," he added at the 28 November briefing.
On the same day as the US soldier's death, US President Donald Trump accused Pakistan of "nothing but lies & deceit" and alleged that the country harboured terrorists.
The US Ambassador to the United Nations Nikki Haley confirmed on Tuesday that the US was withholding $250m (£185m) in aid for Islamabad over its failure to cooperate in the fight against terrorism.
"There are clear reasons for this. Pakistan has played a double game for years," she told reporters at the UN.
"They work with us at times, and they also harbour the terrorists that attack our troops in Afghanistan.
"That game is not acceptable to this administration. We expect far more cooperation from Pakistan in the fight against terrorism."
At the White House, spokeswoman Sarah Sanders echoed Mrs Haley's comments, saying: "Our goal is that we know that they can do more to stop terrorism and we want them to do that".
Mrs Sanders added that the US would announce "specific actions" designed to pressure Islamabad to act in the next 24 to 48 hours.