The Pentagon said two U.S. service members were killed and a third was wounded during a raid against Islamic State militants in their stronghold in eastern Afghanistan.
A U.S. military statement said the U.S. troops were conducting an operation with Afghan security forces when they came under attack Wednesday evening.
"The fight against ISIS-K is important for the world, but sadly, it is not without sacrifice,” said General John W. Nicholson, commander of U.S. Forces-Afghanistan, using an acronym for the Islamic State Khorasan Province group, the local chapter of IS.
The governor of Nangarhar, Gulab Mangal, said the operation, in Achin district's Pekhay area, inflected "heavy casualties" on IS militants. "Around 40 of them were killed and seven arrested," he said.
Earlier this month, a U.S. warplane dropped the largest bomb in America's arsenal on an IS bunker complex in Nangarhar. The strike was described as part of a campaign to destroy the Islamic State Khorasan Province group.
Officials said at least 92 militants were killed in the blast.
Afghan President Ashraf Ghani said Afghan and U.S. forces closely coordinated on the bombing.
VOA national security correspondent Jeff Seldin contributed to this report.