Nine Afghan soldiers have been killed and four others hurt in an air strike by international forces in the eastern part of the country, officials say.

Helicopter gunships reportedly fired on an Afghan army post in Khost province.

The US said Afghan soldiers had been killed and injured in a possible case of “mistaken identity”.

Separately, Afghan security officials say their troops had killed 35 Taleban fighters in a two-day battle in the southern province of Uruzgan.

Three Afghan police are also reported to have died in the firefight.

Afghanistan has seen a surge in violence this year and a number of civilians have been killed by international force air strikes.

Accidental military casualties are rarer than civilian deaths, but several troops have died in recent years in mistaken attacks by both sides.

Local and international forces are battling a fierce Taleban insurgency in much of southern and eastern Afghanistan.

Government concern

Khost official Lutfullah Babakarkheil told Reuters news agency that foreign helicopter gunships had hit an Afghan army post in Dowa Manda district late on Tuesday.

In a statement, the US military in Afghanistan confirmed coalition forces were involved in “multiple engagements” on their return from a previous operation in the region.

“As a result of the engagements, ANA [Afghan army] soldiers were killed and injured.

“Initial reports from troops on the ground indicate that this may be a case of mistaken identity on both sides.”

Col Greg Julian, the chief spokesman for US troops in Afghanistan, said an investigation was under way.

“There was an incident and we are getting together with [Afghan] ministry of defence officials to sort out exactly what happened. A joint investigation will be conducted to get to the truth,” he said.

The Associated Press reports that US and Afghan troops have recently been conducting operations in the region, and the position of the checkpoint was said to be known to US forces.

Earlier this year the US, Afghan government and the UN began a joint investigation to establish the truth about reports that 91 civilians were killed in an air strike on a village in western Afghanistan.

The US concluded that more than 30 people, including women and children, were killed in the strike, which led Afghan President Hamid Karzai to express his concern over the rising numbers of civilian deaths.

Mr Karzai has repeatedly urged foreign forces to exercise more care.