The killings in the eastern province of Paktika came on the same day that one Italian troop died when a grenade was thrown into an armored vehicle in Farah province, in the far west of the country.

The Paktika provincial government issued a statement saying "a verbal dispute erupted" between the Afghan soldier and a US soldier in the district of Khair Kot.

It said the Afghan man killed three US service members and wounded three others before being shot dead himself.

NATO statement confirmed the incident, saying that two US soldiers and one US civilian had died. It gave no further details on the role of the civilian.

Scores of US-led troops have been killed in insider attacks in Afghanistan.

The threat has become so serious that foreign soldiers working with Afghan forces are regularly watched over by so-called 'guardian angel' troops to provide protection from their supposed allies.

So far this year, 85 US-led troops have died in Afghanistan, according to the independent icasualties website. In 2012, 402 died, down from a peak of 711 in 2010.