An Afghan spy agency bodyguard shot dead an American soldier and development worker in a gunfight triggered by a roadside argument Saturday before being killed by return fire.
The shootout in the northern province of Panjsher, one of the most peaceful parts of Afghanistan, is the latest in a series of incidents of Afghan forces turning on foreign troops over recent months.
Panjsher police chief Qaseem Jangalbagh said the Americans were working for the provincial reconstruction team (PRT), which operates alongside military forces on development projects.
"They got into a row with an NDS employee on the road, over what we don't yet know, and during the argument the NDS employee opened fire using his pistol and killed two American PRT workers and another was wounded," said Jangalbagh.
NDS is the National Directorate for Security, Afghanistan's spy agency.
"The NDS employee was also killed in the return of fire," said Jangalbagh, adding that the foreigners were all Americans.
NATO's International Security Assistance Force said one of the ISAF employees killed was a soldier and the other a civilian, adding that the incident was under investigation.
Deputy provincial governor Abdul Rehman confirmed the incident involved PRT workers and ruled out any insurgent or Taliban involvement.
He said the dead NDS employee, named only as Amanullah, was working as a bodyguard for a high-ranking Afghan NDS official and was on his way back to work after a weekend holiday to the province.
Another provincial source said Amanullah was the "special bodyguard" of the deputy Afghan spy chief, Hessamudin Hessam.
"He was an NDS employee and was working as a trusted bodyguard of one of the high-ranking NDS officials. We rule out any enemy role or involvement in this attack," Rehman said.
Incidents in which Afghan soldiers or police officers turn on Western troops are rare, but raise questions about the multi-billion-dollar international effort to train and mentor Afghanistan's security forces.
In July last year a renegade Afghan soldier shot and killed three British army Gurkhas and wounded several others on a base in Helmand province.
In August, an Afghan police officer killed two Spanish paramilitary police officers and a Spanish interpreter during a training session at a base in Badghis province.
A rogue Afghan soldier shot dead foreign troops -- said to be two US Marines -- on a base in the volatile south of the country, in November.
And Afghan National Army (ANA) soldier Shafied Ullah was shot dead while on the run last month after allegedly killing 25-year-old Australian Lance Corporal Andrew Jones as they shared guard duties at a patrol base.
Taliban insurgents claimed Saturday's attack and said they killed three PRT members and wounded another four in an ambush. The Taliban are known to exaggerate their claims.
Although the area is usually free of deadly violence, an Italian anti-drug specialist, Lt. Col. Cristiano Congiu was shot and killed in Panjsher by angry locals following a argument that resulted in an exchange of fire.
Congiu, 50, was travelling with an American woman and a translator to visit the local emerald mines.
The province is one of the first wave of seven places due to transition from foreign to Afghan security control around July, a process which should eventually lead to a full foreign combat troop withdrawal from Afghanistan in 2014.
Officials in Panjsher are trying to promote it as a tourist destination, focusing on its spectacular natural beauty and legacy as a bastion of resistance against the Taliban and the Soviet Union during the 1980s.