KABUL — An American civilian engineer has been found murdered in mysterious circumstances in Kabul a few days before the 10-year anniversary of the 9/11 attacks that triggered the long war in Afghanistan.

Afghan and Western security sources told AFP Tuesday that the man's body was found on Monday and an investigation was under way.

"An American national has been found dead in Kabul's district 12," an Afghan intelligence official told AFP.

Asked if he was murdered, the official said "Yes." Speaking on condition of anonymity as he was not authorised to speak to the media, he gave no further details.

A Western security official confirmed the incident and said the man had been murdered.

NATO's coalition force in the country said late on Monday that "a US Department of Defense civilian employee had died in eastern Afghanistan" but gave no further details.

A spokesman for the interior ministry said it was not aware of the incident.

Kabul police chief Mohammad Ayoub Salangi said he had no information and that the NDS, Afghanistan's spy agency, would have been "handling it".

Kabul city is under the control of Afghan security forces, along with most of the wider Kabul province and six other parts of the country that were handed over by NATO-led troops in July.

In recent months Kabul has been hit by several high-profile suicide and gun attacks including a deadly assault on the British Council building in the west of the city two weeks ago.

The murder of the US engineer comes five days before the 10-year anniversary of the 9/11 attacks that led to the US-led invasion of Afghanistan in October 2001 to topple the Taliban government, which had sheltered Al-Qaeda leaders responsible for the attacks.

The US-led NATO force has since been fighting an Islamist insurgency being waged by the remnants of the Taliban.

The insurgency, which largely relies on roadside bombs and suicide attacks, has reached its deadliest phase over the past two years.

It is not clear whether the US engineer was abducted before being found dead. According to the Afghan intelligence official, his body was found in an area of Kabul where foreign forces have military bases and other installations.

The rebels have in the past used abduction of foreign citizens and high-profile Afghans as a pressure tool on the US-backed government of Afghanistan, and have killed some of their hostages.

Criminal kidnapping motivated by ransom is also common in Afghanistan but most victims are rich Afghans.