KABUL: A Nato helicopter crashed in Afghanistan on Wednesday, killing two US troops in an area south of Kabul that is largely under Taliban control, officials said.

The Islamist militia leading a decade-long insurgency against foreign troops claimed to have shot down two helicopters in Logar province, but Nato said the cause of the crash was under investigation.

The militants are known to make exaggerated claims.

“An ISAF helicopter has crashed in eastern Afghanistan, resulting in two ISAF fatalities. We are investigating,” a spokesman for Nato's US-led International Security Assistance Force told AFP.

In Washington, a US defence official, who spoke on condition of anonymity, later said the two troops killed were Americans and that the aircraft that went down was a small, single-engine OH-58 helicopter.

The administration in Logar said the area, 13 kilometres (eight miles) north of the provincial capital Puli Alam, is mostly controlled by the Taliban.

“There was a helicopter incident in Baboos area, which is an area largely under Taliban control,” said provincial spokesman Din Mohammad Darwish.

The area was “inaccessible” to Afghan forces, he added.

In a statement on their website, the Taliban claimed to have used rockets to shoot down two American helicopters, killing “tens of invaders”.

Logar has become an increasing flashpoint for violence.

On Wednesday, defence ministry spokesman, Zahir Azimi, admitted that security challenges have increased in Logar and neighbouring province Wardak, but said there was a plan to deal with it.

ISAF had earlier on Wednesday announced that a Taliban leader wanted for an August 7 truck bombing of a Nato base in Logar had been killed in an air strike in Puli Alam on Tuesday.

The military said it believed the Taliban operative had been planning another large-scale attack.

Helicopter crashes are fairly frequent in Afghanistan, where the 130,000-strong Nato mission relies heavily on air transport.

On August 16, a Black Hawk came down in the southern province of Kandahar, killing seven American soldiers and four Afghans, for which the Taliban also claimed responsibility.

In August 2011, an American Chinook was shot down by the Taliban near Kabul, killing eight Afghans and 30 Americans, including 22 Navy SEALs from the same unit that killed Osama bin Laden in neighbouring Pakistan earlier that year.

It was the deadliest single incident for American troops in 10 years of war in Afghanistan.