The incident occurred Wednesday when a US and Afghan patrol came under fire near an Afghan army post on the outskirts of Tarin Kot, the capital of Uruzgan province, a NATO spokesman in Kabul told AFP.

They called in airstrikes which hit the army post, killing five and seriously wounding a further 10 Afghan soldiers, said Karim Karimi, deputy head of the Uruzgan provincial council.

"As the American patrol approached the base, the ANA (Afghan National Army) soldiers probably thought it was the Taliban approaching them," he told AFP.

Large parts of Uruzgan province remain under the Taliban control. In recent years the militants have also made repeated incursions into the provincial capital.

Seventeen soldiers had been at the post in total, with only two managing to flee unhurt, Karimi said.

The Afghan defence ministry confirmed the toll, saying that Afghan and US forces had been conducting a "joint operation" in the area at the time.

"Because of a lack of proper coordination of the army, an ANA post was hit," a ministry statement said, adding that an investigation is ongoing.

The NATO spokesman said the US had carried out "precision self-defense air strikes on people firing on Afghan and American forces conducting a ground movement near an ANA check point in Tarin Kot".

"The strikes were conducted after Afghan and US forces came under effective small arms and rocket propelled grenade fire and requested air support in self-defense," a spokesman told AFP by email.

"Afghan and US forces attempted to de-escalate the situation but they continued to be fired upon. We are operating in a complex environment where enemy fighters do not wear uniforms and use stolen military vehicles to attack government forces."

"I counted that the planes were shooting at the base for some 30 minutes," Haji Lal Agha, a local resident, told AFP over the phone.

Incidents known as "friendly fire" are not unheard of in Afghanistan, and have bred deep mistrust between local and foreign forces.

In one of the deadliest, 16 Afghan policemen were killed in July 2017, when they were mistakenly targeted by US airstrikes in neighbouring Helmand province.