The United States military says it is still unclear what caused one of its helicopters to crash in Afghanistan killing five American soldiers.
US troops are deployed in remote regions
Seven others were injured in Sunday's crash near Bagram air base, US Central Command said in a statement.
Locals said they had seen the crash, but were not sure what caused it.
Helicopters from the base have been used in a US offensive against suspected al-Qaeda and Taleban members in remote areas of the country.
"The cause of the crash is unknown and under investigation," the Central Command statement said.
Villagers near the crash site said they heard a loud bang and saw the helicopter's tail fall off before the aircraft hit the ground and burst into flames.
"We did not hear any shooting," one man told the Reuters news agency.
But another man quoted by the Associated Press could not say whether the helicopter had been hit by a missile or not.
Operation Mountain Resolve is aimed at destroying bases used by militants linked to al-Qaeda and other groups in the wild region of Nuristan and Kunar.
Central Command said the troops aboard the downed helicopter were supporting Operation Mountain Resolve.
US war planes are also involved, called in by the troops on the ground.
But the US military has found it hard to locate al-Qaeda, the BBC's security correspondent Frank Gardner says.