Two soldiers and a civilian, all American, have been killed in a so- called ‘insider attack’ following an argument with a man in Afghan army uniform.
The attack happened in the eastern province of Paktika.
It follows the death of an Italian soldier in the west of Afghanistan earlier.
In that incident, three Italians were also wounded when an 11- year-old threw a grenade at NATO troops.
The dead soldier is being named as 31-year-old Giuseppe La Roda.
Reports indicate the Italian troops were on foot patrol in the town of Farah at the time.
It demonstrates how widespread the danger is to International Security Assistance Force troops.
Insider attacks, where Afghan security forces have turned on NATO force allies are becoming increasingly common. Last year this led to some joint operations being curtailed.
16 NATO troops have died in Afghanistan this month.