An explosion hit a convoy of NATO-led troops in eastern Afghanistan on Tuesday, the alliance said, and residents said they saw three victims being carried away from the wreckage.
The private Tolo TV channel said two U.S. soldiers were killed and one wounded in the attack, which it said was carried out by a suicide bomber.
A NATO official in Kabul confirmed there had been a blast, but had no details on the incident.
The attack occurred close to a NATO base in Khost province, which borders Pakistan. Most troops in eastern Afghanistan are American.
Residents said they saw three NATO soldiers being carried away, but it was not immediately clear whether they were dead or wounded.
Afghanistan is in the grip of the worst violence since the Taliban was toppled from power in late 2001.
Taliban fighters and their allies have made a comeback in the last two years in their campaign to drive out foreign forces and topple the Afghan government.
PHOTO CAPTION
File image of US and NATO soldiers taking cover from dust and debris from a helicopter in the rugged Spira mountains in Khost province, along the Afghan-Pakistan border.
Reuters