Afghan soldier
Afghan National Army soldiers keeps watch near the site of an incident in Kabul.

A member of Afghanistan's security force has attacked an Australian Nato base, killing three troops and injuring a further two.

It was the second attack in a day and brought the number of Australian soldiers killed recently to five.

The attack happened in the province of Uruzgan, a Nato base in southern Afghanistan. Local reports have confirmed the assailant was wearing an Afghan National Army uniform, and began shooting while troops were relaxing around the base.

The troops returned fire, but the assailant was able to climb a fence and escape.

Australian forces have now suffered three "green on blue" attacks within a year. The name for such assaults refers to the fact that Afghan insurgents typically wear green uniforms, while Nato troops wear blue.

Australian veterans affairs minister Warren Snowdon said: "Three Australian solders have been killed as a result of a green-on-blue incident and two have been injured."

Snowdon said the incident was a tragedy. "This loss of life is unacceptable and unnecessary," he said.

About 1,550 Australian troops are based in Afghanistan, constituting the largest military presence of any country outside Nato. The Afghan war has claimed 36 Australian lives in total.

Insider attacks are a major problem faced by Nato troops as they prepare for withdrawal from Afghanistan by the end of 2013.

According to Isaf data, 45 lives have been claimed in over 30 attacks in 2012 - about 14 percent of the overall death toll.