US military officials in eastern Afghanistan say they believe troops on the ground when a US helicopter crashed in Konar province are still alive.
The Chinook was brought down by a rocket-propelled grenade, described as “a lucky shot” by US commanders.
The Taleban say they shot down the aircraft, which was carrying troops to help a reconnaissance unit in the area.
All 16 soldiers on board died, in the US’s worst single combat-related loss since invading Afghanistan in 2001.
The Chinook is the first US helicopter to be shot down in Afghanistan since March 2002.
The BBC’s Andrew North at the main US base in eastern Afghanistan says officials there have strong hopes the reconnaissance unit members have not been killed or captured.
Officials told the BBC they had “several indications” that the troops on the ground were still alive, but they would not say what those indications were.
Neither would they say why the unit had not yet been brought to safety. In Kabul, US military spokesman Col Jim Yonts said: “We do not have eyes on them right now, but there is no reason to believe that they are dead.”
He said the Chinook had been sent in after the reconnaissance team requested support, but the unit was not at the location when the helicopter arrived.
Col Yonts would not confirm or deny a Taleban claim that the militants had killed seven US “spies” before the MH-47 helicopter was shot down.
A number of Afghan guides working with the US military are also missing.
The Pentagon said eight soldiers from airborne special forces units and eight navy Seal commandoes were killed in Tuesday’s crash.
It said 16 people had been on board, not 17 as originally reported.
All bodies have been recovered, and the remains are being identified.
Officials say they are still investigating the exact reason why the helicopter came down.
Our correspondent says it seems to have crashed at some distance from the point where it is believed to have been hit by at least one unguided rocket-propelled grenade.
Twin-engined aircraft with two, three-bladed rotors
Used to move soldiers, weapons and supplies
Can carry 54 troops or 25,000 lbs (11,340 kg) of freight – more than its own weight
Crew of four
Speaking in Washington, Lt-Gen James Conway, director of operations for the joint chiefs of staff, confirmed that the military believed the Chinook had been hit by a rocket-propelled grenade.
“Indications are that it was an RPG, which is a pretty lucky shot, honestly, against a moving helicopter,” he told reporters.
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 forces have been engaged in a number of combat missions in south-east Afghanistan against suspected Taleban and al-Qaeda militants and their allies opposed to the Kabul government.
US military forces regularly come under attack in Konar province.
There has recently been an increase in fighting between US-led troops and militants.
On Tuesday, Nato’s military head, Gen James Jones, met Afghan President Hamid Karzai to discuss plans for the alliance to take over security across southern Afghanistan next year, gradually relieving the American force.