Three Australian troops in the NATO-led force in Afghanistan have been killed in an attack by a member of the Afghan security forces, officials said, in the latest insider attack that has caused growing dismay among coalition commanders.

The assault occurred in southern Uruzgan province in the evening ofn Wednesday, a US defence official, who spoke on condition of anonymity, said.

About 1,500 Australian troops are deployed in the province as part of the International Security Assistance Force (ISAF).

"An individual wearing an Afghan National Army uniform turned his weapon against International Security Assistance Force service members in southern Afghanistan yesterday, killing three," ISAF said in a statement.

"The incident is currently under investigation."

NATO has struggled to counter the so-called green-on-blue attacks in which uniformed Afghans turn their weapons against their international allies.

The scale of insider attacks by Afghan troops is unprecedented in modern warfare and threatens to derail the West's carefully laid withdrawal plans, analysts say.

The assaults have surged this year, with more than 30 attacks claiming the lives of 45 coalition troops, mostly Americans, comprising about 14 per cent of the overall death toll in the war for 2012, according to ISAF.

Green-on-blue attacks

August has been the worst month for so-called green-on-blue attacks in Afghanistan in more than 10 years of war, with nearly one in three international coalition deaths caused by Afghan allies.

The violence has troubled the international force, which has portrayed its partnership with Afghan troops as the key to a planned withdrawal of foreign combat troops over the next two years.

Roadside bombs cause majority of deaths in 2012

The commander of NATO forces in Afghanistan, US General John Allen, said last week the causes of the surge in insider attacks were varied, and that Taliban infiltration only accounted for about a quarter of the incidents.

He said the recent spate of assaults may have been related to the Muslim holy month of Ramadan, when Afghan soldiers were under strain from fasting in intense heat while engaged in combat.

A Pentagon assessment last year found serious tensions between the coalition forces and their Afghan counterparts, with relations plagued by cultural clashes and deep mistrust.

Afghan politician Abdullah Abdullah, a former foreign minister and potential presidential candidate in 2014 elections, points to problems within the government as a reason for the attacks.

He takes President Hamid Karzai to task for what he calls his "vague" message in which he regularly calls the Taliban "brothers", urging them to talk peace, and criticises the US.

"Sometimes you don't know who he calls the enemy - the Taliban or the Americans," Abdullah told AFP news agency.

Source: Al Jazeera and agencies