An Afghan soldier has been killed at a military base in the capital Kabul, after shooting at international troops.
The incident, which injured at least one foreign soldier, began after an argument, Nato officials said.
It is the fourth such attack in a month. Last year, attacks by Afghan servicemen on their Nato colleagues accounted for around 15% of all international troop casualties.
More than 100 international soldiers have been killed this year.
In June, Nato handed over security for the whole of Afghanistan to Afghan forces, but some 97,000 troops remain.
The Nato-led International Security Assistance Force Isaf currently has troops from 50 contributing nations - most of them, some 68,000, from the US - providing military back-up when needed.
By the end of 2014 all combat troops should have left to be replaced - if approved by the Afghan government - by a smaller force that will only train and advise.
Most Nato soldiers have died in insurgent attacks, but the pressure on contributing nations to withdraw has been exacerbated by a series of "green-on-blue" attacks in which members of the Afghan security forces have killed coalition troops.
At least 60 Nato personnel died in such attacks in 2012. Many more Afghan security force members have died at the hands of their colleagues, in so-called "green-on-green" attacks.
New measures to reduce the insider attacks, including the presence of guards around international troops and reducing the number of weapons Afghan troops there are allowed to carry, have had an impact, says the BBC's David Loyn in Kabul.
But the international troops remaining have to train and mentor Afghan forces and they cannot do that without staying in close contact with armed Afghan soldiers, our correspondent says.