A U.S. service member was killed in a "combat engagement" in Afghanistan's Nangarhar province on New Year's day, and four other U.S. service members were injured, according to a U.S. military statement.The U.S. military did not immediately explain what kind of combat the service members were engaged in at the time, and whether they were fighting ISIS or the Taliban.Two of the injured service members are receiving medical treatment nearby. They're in stable condition, the military says, and the two others "have returned to duty.""We are deeply saddened by the loss of one of our own," said Gen. John Nicholson, the top commander of U.S. forces in Afghanistan. "At this very difficult time our heartfelt sympathies go out to the families and friends of our fallen and wounded brothers."This area, along Afghanistan's border with Pakistan, has been particularly deadly for U.S. troops in the past year, NPR's Tom Bowman reports. "Of the 15 Americans killed in the country last year, eight were killed in Nangarhar, seven of them by hostile fire." U.S. troops and Afghan allies have been fighting Islamic State militants in the area for two years, he adds."Most of the 11,000 Americans work inside bases training Afghans, but some American special operations forces go on combat missions, accompanying Afghan commandos on raids against ISIS and Taliban fighters," Tom reports. "This year, more American soldiers are expected to head out on operations with Afghan units against the Taliban."President Trump recently committed more U.S. troops to Afghanistan without a specific timetable. As we have reported, "the recent commitment of about 3,000 additional troops will bring the total number of U.S. service members in Afghanistan to between 14,000 and 15,000," according to the Special Inspector General for Afghanistan Reconstruction. Copyright 2018 NPR. To see more, visit http://www.npr.org/.