NATO contractor killed in Afghan 'insider attack'

"The civilian died when three individuals wearing Afghan uniforms and driving an Afghan security force vehicle forced their way into the base in eastern Afghanistan," a spokesman for the NATO-led force said.

The spokesman said that all three of the attackers were killed by Afghan and ISAF (International Security Assistance Force) troops but added that no other details were available as an assessment of the attack was still under way.

Afghan officials, who declined to be named, said the incident occurred in the Tagab district of Kapisa province.

NATO soldiers are fighting alongside Afghan colleagues to thwart Taliban militants, but more than 60 foreign soldiers were killed in 2012 in "insider attacks" that have bred mistrust and threatened to derail the training process.

If the attackers are confirmed to be Afghan soldiers or police, it would be the first insider attack since January when a British soldier was shot dead by an Afghan soldier in the Nahr-e Saraj district of Helmand province.

A text message from the Taliban did not claim responsibility for Friday's attack but claimed that two Afghan army soldiers had killed nine American soldiers.

The militants regularly exaggerate death tolls and NATO officials say that most "insider attacks" stem from personal grudges and cultural misunderstandings rather than Taliban plots.

The threat of insider attacks has become so serious that foreign soldiers working with Afghan forces are regularly watched over by so-called "guardian angel" troops to provide protection.