An Afghan soldier shot and killed two Nato soldiers at a base in southern Afghanistan today.
The man was then shot dead by other troops at Lashkar Gar in Helmand Province.
The attack was the latest in a string of "green on blue" attacks in which Afghan security forces have turned their guns on their international colleagues or mentors. Such attacks have become increasingly common over the past year, particularly since the burning of Korans at a US base in February.
Fifteen Nato service members have been killed by Afghan security officials or militants disguised in their uniforms so far this year.
Ghulam Farooq Parwani, deputy commander of the Afghan National Army in Helmand, said the shooter was from the eastern Nangarhar province and had been in the army for four years. The Afghan soldier arrived at the gate of the base in an army vehicle. He was able to get close to the Nato troops by claiming that he had been assigned to provide security for a delegation of government officials from Kabul who were visiting the base.
"He got close to the foreign troops - three or four meters - and he opened fire," Mr Parwani said. "Then the foreign troops killed him."
A Taliban spokesman said the shooter was an Afghan soldier who was in close contact with insurgents and had notified them of his planned attack before carrying it out.
Since 2007, Afghan security forces have killed more than 75 Nato service members and wounded more than 110 others, according to the Pentagon. More than 75% of the attacks have occurred in the past two years.
Five British soldiers were killed by a rogue Afghan policeman in November 2009. The gunman opened fire on the men in a military compound in Nad e-Ali before fleeing. The Taliban later claimed responsibility.
The latest attack also comes two weeks after a US soldier allegedly went on a pre-dawn shooting rampage in neighbouring Kandahar province, killing 17 people and wounding six.
The Lashkar Gah base is dominated by British forces.
The Ministry of Defence said it was aware of the incident, but refused to release any more details or say whether the soldiers were British.
The killings come at a time when international troops have stepped up training and mentoring of Afghan soldiers, police and government workers so that Afghans can take the lead and the foreign forces can go home.
The success of the partnership, which is the focus of the coalition's exit strategy, is threatened by the rising number of Afghan police and soldiers - or militants disguised in their uniforms - who are turning their guns on their foreign allies.
Six American troops were killed in what were believed to be revenge attacks for the burning of the Korans, although it is impossible to know the exact motive because most the shooters were killed in the incidents.
The US apologised for the burning, saying the Islamic texts were mistakenly sent to a rubbish burn pit at Bagram Air Field, north of Kabul. But the incident raised what had been simmering animosity toward outsiders to a full boil. Deadly protests raged around the nation for six days - the most visible example of a deep-seated resentment bred by what Afghans view is a general lack of respect for their culture and religion.