A U.S. service member was killed on Tuesday by a roadside bomb in Afghanistan's Helmand Province, the military said in a statement.
Another American troop was injured in the attack near Lashkar Gar, along with six Afghan soldiers, according to a statement from the NATO-led mission in the country.
The name of the service member who died wasn't released, pending notification of family members, the release states. The individual was killed while conducting an operation with Afghan forces when their patrol triggered an improvised explosive device, or IED, it states.
"On behalf of all U.S. Forces-Afghanistan, as well as Resolute Support, our deepest sympathies go out to the families and friends of those involved," Gen. John W. Nicholson, commander of USFOR-A and Resolute Support, said in the statement. "We are deeply saddened by this loss, but remain committed to helping our Afghan partners provide a brighter future for themselves and their children."
Defense Secretary Ashton Carter said he was "deeply saddened" to learn of the casualties. "My thoughts and prayers are with the loved ones of the service member killed and all those injured," he said in a statement.
"This tragic event in Helmand province reminds us that Afghanistan remains a dangerous place, and there is difficult work ahead even as Afghan forces continue to make progress in securing their own country," he added. "We will continue to work closely with the government of Afghanistan and our NATO partners to bolster the capabilities of the ANDSF so they can provide the people of Afghanistan the peace they deserve."
The attack came a day after the U.S. military announced it sent 100 troops to the defense of Lashkar Gah, the capital of embattled Helmand province that's in danger of falling to the Taliban.
The U.S. troops are in a training and advisory role to the Afghan National Defense Security Forces and will provide a "new presence to assist the police zone" in Lashkar Gah, Army Brig. Gen. Charles Cleveland, chief spokesman for Nicholson, said in a statement.
In a briefing to the Pentagon late last month, Nicholson said the Afghan Security Forces' 215th Corps had made progress in Helmand since cashiering corrupt leaders, but Cleveland made no attempt to downplay the seriousness of the situation in the province or the threat to Lashkar Gah.
"This is a big effort by the Taliban. This is probably the most serious push we've seen of the season," Cleveland said. He described the troop deployment as a "temporary effort" to advise the Afghan police, but he declined to put a timeline on how long they would stay.
Tuesday's attack marks the second combat death this year of a U.S. service member in Afghanistan -- both of which occured in Helmand province, less than 30 miles apart.
Staff Sgt. Matthew Q. McClintock, 30, a U.S. Army Special Forces soldier assigned to the 1st Battalion, 19th Special Forces Group (Airborne), based in Buckley, Washington, was killed Jan. 5, during an extended firefight in Marjah, Afghanistan.
Two other American troops were wounded during the January operation to assist Afghan forces in taking back territory from a resurgent Taliban in the southwestern part of the country.
A total of eight coalition troops have been killed in Afghanistan this year, including six Americans and two Romanians, according to NATO and the website iCasualties.org, which tracks military deaths in Iraq and Afghanistan. Half of those killed in country were from non-hostile actions.
President Barack Obama in July announced a change in plans for U.S. troop levels in Afghanistan when he said 8,400 American service members would stay in the country into next year, leaving it up to his potential successor Donald Trump or Hillary Clinton to decide on the size of the military footprint there.
The president initially planned to reduce the U.S. troop presence in Afghanistan to 5,500 before he left office but changed course after a recommendation from Nicholson. The current authorized level of U.S. troops in Afghanistan through the rest of the year stands at 9,800.
The American forces are split between two missions that will continue -- NATO's Resolute Support mission to advise Afghan security forces and the separate Freedom's Sentinel.
-- Richard Sisk contributed to this report.