The Afghan army said on Wednesday that it has sacked or arrested hundreds of soldiers over alleged links to insurgent groups.
There is growing concern amongst Afghanistan’s allies about the increase in so-called inside attacks on NATO troops.
An Afghan serviceman shot dead three Australian soldiers in the country’s southern Uruzgan province last week.
General Zahir Azimi, a defence ministry spokesman, said Kabul and NATO, are working on a joint investigation.
“This is a big concern for the Afghan president and the defence ministry,” he told reporters.
Forty-five NATO troops have been killed by their Afghan counterparts so far this year, compared with 35 in 2011.
It has raised doubts about whether Afghanistan’s military will be able to take over security responsibility from NATO in 2014.