An Afghan soldier shot dead his Australian mentor at a guard tower in Afghanistan, an official says.
The death was one of two Australian fatalities on Monday that brought Australia's toll in the conflict to 26, said Australia's Defence Force chief, Air Chief Marshal Angus Houston.
The killer had fled the scene and was being hunted by his Afghan National Army colleagues, Houston said.
The dead soldier, a 25-year-old army lance corporal, had been on guard duty with his killer at Patrol Base Marshal in the Chora Valley in Uruzgan province.
Houston said he could not release any details of the killer's motivation, but said the tragedy was not an accident.
"This incident is obviously going to quite rightly raise some very serious questions about the security measures that we have in place," Houston told reporters.
Australia has 1550 soldiers in Afghanistan with a primary focus on training an Afghan National Army battalion to take responsibility for security in restive Uruzgan.
Houston said the "rogue soldier" was the first to turn on his Australian mentors.
The second fatality was a 27-year-old army lieutenant killed when a Chinook helicopter crashed while on a resupply mission 90km east of the Australian base in Tarin Kot in Uruzgan.
None of the five other Australians aboard was seriously injured, Houston said.
The army is informing the dead soldiers' relatives before their names are made public.
Houston had told a Senate committee on Monday that the Taliban's momentum in Afghanistan had been halted by sustained offensives by international forces through the winter months.
He said the size of the Afghan forces, which had grown by 79,000 to 270,000 in the past year with the aid of Western mentors, was a major positive.
