Six US marines were killed in a helicopter crash in southern Afghanistan on Thursday, according to a US official, but Nato claimed Taliban fighters were not active in the area at the time.
"The cause of the crash is under investigation. However, initial reporting indicates there was no enemy activity in the area at the time of the crash," a spokesman for the Nato-led International Security Assistance Force said on Friday, raising questions about a possible malfunction or pilot error.
The Nato spokesman declined to confirm the nationality of the victims but a American official, speaking on condition of anonymity, said all of the dead were US marines.
It is the worst crash since August last year when 30 US forces, including 22 elite Navy Seal commandos, died when their helicopter came down in eastern Afghanistan.
An investigation into the incident confirmed the Taliban fired a rocket-propelled grenade that hit one of the helicopter's rotary blades and exploded, sending it plunging to the ground and bursting into flames within seconds. All eight Afghans on board were also killed.