An unguided rocket-propelled grenade brought down the US Chinook helicopter that crashed in Afghanistan on Tuesday, US commanders believe.
The troops were flying to join an operation against militants
Lt-Gen James Conway told reporters that the attack was a "pretty lucky shot, against a moving helicopter".
All the 16 soldiers on board the helicopter died when it crashed on its way to the eastern province of Konar.
The Taleban say they shot down the aircraft, which was carrying soldiers to join operations against militants.
The Chinook is the first US helicopter to be downed in such a way in Afghanistan since March 2002.
US military officials told the BBC's Andrew North at the main US base in eastern Afghanistan that there are still strong hopes that soldiers who were on the ground when the Chinook crashed are alive.
Pentagon officials have confirmed that all 16 bodies the helicopter have been recovered and the remains were being identified.
US troops reached the crash site in a remote mountain valley late on Wednesday night.
Bad weather had hampered the search, which has been further complicated by the high altitude of the crash site and continued threat of further militant attacks.
US military spokesman Lieutenant Colonel Jerry O'Hara told the Associated Press that "there are still bad guys in the area" around the crash site.
He said the soldiers were engaged in a "recovery and tactical operation at the same time".
US forces have been engaged in a number of combat missions in south-east Afghanistan against Taleban and al-Qaeda militants and their allies opposed to the Kabul government.
A man claiming to be a spokesman for the Taleban told the BBC its supporters had shot the helicopter down.
He said he had video of the crash and its aftermath but our correspondent says there is still no sign of it.
A second man also claiming to speak for the Taleban phoned two international news agencies in Afghanistan with similar claims.
US military forces regularly come under attack in Konar province.
There has recently been an increase in fighting between US-led troops and militants.