Another seven soldiers are unaccounted for, some of them soldiers who were fighting on the ground.

The Taleban say they shot the Chinook down. The US concedes that "hostile fire" may have been the cause.

The Chinook was taking the soldiers to join operations against militants in the eastern province of Konar.

Officials say there is still hope that some of those unaccounted for are alive.

But the BBC's Andrew North who is at the main US base in eastern Afghanistan says they may also have been captured.

US forces have been engaged in a number of operations in south-east Afghanistan against Taleban and al-Qaeda militants and their allies opposed to the Kabul government.

If the reports of hostile fire are confirmed, the Chinook would be the first US helicopter to be downed in such a way in Afghanistan.

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.

Officials say the rugged mountain terrain had made it difficult for the rescue team to access the area.

Rebel claims

Earlier, the governor of Konar province, Asadullah Waffa, told the BBC the helicopter had been brought down by a rocket.

He said the attack was the work of well-funded militants who had entered Afghanistan planning to spread chaos before September's parliamentary elections.

His security forces recently arrested two such militants posing as cameramen, he said.

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 different man who said he spoke 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.