At least 10 Afghan civilians, including eight schoolchildren, have been killed in fighting involving Western troops, President Hamid Karzai has said.
Mr Karzai said the deaths occurred during military operations in eastern Kunar province two days ago.
Kunar governor Sayed Fazlullah Wahedi told the Reuters news agency officials could not visit the area "because of the presence of the Taliban".
Nato said it had no record of operations or deaths in the area.
A brief statement from Mr Karzai's office said initial reports indicated the civilians had died in "a series of operations by international forces" on Saturday.
It said he "strongly condemns the operation which caused civilian deaths and has appointed a delegation to investigate the incident".
The AFP news agency quoted a senior Afghan official as saying the death toll could change as investigations take place.
An unnamed Western official told AFP that US special forces had been conducting operations in the area, close to the border with Pakistan, and had killed and captured "a lot of Taliban".
He said the operations were being carried out independently of the Nato-led and coalition forces in Afghanistan.
Civilian deaths at the hands of foreign troops have led to widespread anger among Afghans.
Kunar province is remote and dominated by the Taliban
Mr Karzai has previously said such deaths are damaging to the fight against militancy.
The BBC's Peter Greste in Kabul says Kunar province is remote, snowbound and dominated by the Taliban, so the investigation into Saturday's alleged incident will be difficult.
But if the civilians deaths are confirmed, it will be a blow to Gen Stanley McChrystal, the commander of Nato forces in Afghanistan, who has vowed to limit such casualties, says our correspondent.
Also on Monday, militants were reported to have stormed a police checkpoint in north-western Badghis province.
Two police officers were killed and three are missing, said local officials.