Eight American soldiers and a US contractor have been killed by an Afghan military pilot who opened fire on them at an airport in Kabul.
The shooting suddenly started in the middle of a meeting in an operations room.
The pilot also died in the attack, the latest - and deadliest - in a string of attacks on foreigners inside military or government installations in Afghanistan.
There are nearly a quarter of a million Afghan security forces and 130,000 NATO-led coalition troops. Given the numbers involved, the BBC reports, it's still rare for an Afghan soldier to turn his gun on the men he serves with.
In the past two years, 42 foreign troops have died at the hands of Afghans they were mentoring, or Taliban dressed in police or army uniform.
These incidents resonate widely, the BBC's correspondent in Kabul says, and are bad for morale. American and British soldiers say that they must remain on their guard - that they can never fully trust the Afghan soldiers and police they serve with.
A senior Afghan security official told the BBC the pilot, Gul Ahmad, was suffering from "mental illness" and either got into a fight with his foreign colleagues or planned the attack after being recruited by the Taliban.