NATO forces have mistakenly killed eight Afghan soldiers and police in an air strike during a battle while searching for two missing American soldiers in Afghanistan.

The NATO-led force said none of its troops were killed but five were wounded, along with at least 20 Afghans, in a battle that took place during a manhunt for the two soldiers who went missing on Wednesday (local time).

Those killed include four Afghan soldiers, three policemen and another person believed to have been an interpreter.

"Yesterday, in a NATO air strike, seven Afghan [soldiers and police] were martyred in Badghis province," Afghan Defence Ministry spokesman General Zaher Azimy said.

Lieutenant Todd Vician, a NATO spokesman, confirmed that NATO had launched air strikes during the search operation but said it was still investigating whether its strikes were responsible for friendly casualties.

The battle took place during a search and rescue operation for two soldiers from the US 82nd Airborne Division who went missing after a resupply mission.

The Taliban and provincial officials in Badghis say the two missing Americans drowned in a river. A Taliban spokesman has said the militants recovered their bodies.

NATO says the search is still under way.

Reports of missing soldiers in Afghanistan are rare and prompt a large-scale military response.

Troops from more than 40 nations are members of the nearly 110,000-strong NATO-led force, two-thirds of them American.

- Reuters