At least eight Afghans working with US forces have been killed in a Nato air strike in north-western Afghanistan, the defence ministry in Kabul says.
Nato confirms an air strike was ordered and is investigating whether it was the cause of the deaths on Friday.
It was launched as US and Afghan forces reportedly came under insurgent attack during search operations in Badghis province for two missing US soldiers.
Five Americans and 18 Afghans were also wounded on Friday.
Nato said the casualties occurred "during a joint operation that involved multiple engagements over several hours".
'Important mission'
The Afghan defence ministry said a base housing coalition troops and Afghan security forces was mistakenly hit by the air strike.
Four Afghan soldiers, three police and another person believed to have been an interpreter were killed.
A spokesperson for the Nato force, US Navy Capt Jane Campbell, said: "We are saddened by the loss of life and injuries sustained during this very important mission."
The Afghan deaths come days after an Afghan policeman killed five British troops in Helmand province, who the soldiers had been training.
The BBC's Andrew North in Kabul says that incident provoked fears about the possibility of Taliban infiltration into Afghanistan's armed forces.
Officials have said they believe the two US soldiers missing in western Afghanistan after failing to return from a routine resupply mission have drowned.
Afghan officials say the men, who were from 82nd Airborne Division, died two days ago in what appears to have been an accident.
Police said they died trying to recover supplies dropped by Nato aircraft which had fallen into a river.
A Taliban spokesman told Reuters news agency that they recovered the bodies in Badghis province.
Soldiers from more than 40 countries are taking part in Nato's force of nearly 110,000 troops in Afghanistan, two-thirds of them from the US.
Western Afghanistan has recently seen a rise in violence, with Taliban insurgents planting roadside bombs to maximise fatalities. This year more than 400 troops have been killed, most of them Americans.
