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

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.

Most of the dead are Americans, but the latest to die were three Australian troops killed by a member of the Afghan security forces in southern Uruzgan province on Wednesday.

The assaults have spiked this year, with more than 30 incidents claiming the lives of 45 coalition troops, making up about 14 per cent of the overall death toll in the war for 2012.

Analysts and officers agree that no other modern war, including those in Vietnam and Iraq, has seen so many cases of allies turning their weapons on international troops, but wrestle with the reasons for the phenomenon.

Taliban insurgents claim responsibility for many of the attacks, saying their fighters have infiltrated the Afghan army and police, but Nato says the majority of the incidents are due to cultural differences and personal animosities.

The spike in attacks has alarmed the US-led Nato force to the extent that all soldiers have been ordered to be armed and ready to fire at any time, even within their tightly protected bases.

That level of distrust undermines Nato's plans to work increasingly closely with Afghan forces as they prepare to hand over responsibility for security ahead of the withdrawal of their 130,000 troops by the end of 2014.

“I believe (the scale of the insider attacks) is unprecedented in the history of war,” Fabrizio Foschini of the Afghanistan Analysts Network told AFP.

“It is one of the developments that Isaf is most concerned about because it represents both a military setback on the ground and it conveys a very negative perception to home public opinion.”

Foschini agrees with Nato's assessment that most attacks are due to cultural differences, and points out that many Afghans say they got on better with Russian soldiers during the Soviet Union's 10-year occupation in the 1980s.

The religious divide is also part of the picture, Foschini says, and some observers have linked the increase in attacks to the burning of Qurans at a US military base in February this year.

But “the polarisation between who is a foreigner and who is an Afghan is becoming bigger because of the prolonged war and prolonged foreign presence, which is raising some hostility”, he says.

Apart from the Quran burning, the image of US troops has taken a battering this year through pictures and videos showing soldiers abusing the bodies of the dead and a massacre of civilians by a rogue American trooper.

Nick Mills, an associate professor of journalism at Boston University who served as a combat photographer for the US Army in Vietnam, also said he believed the green-on-blue attacks “have no parallel in recent military history”.

“The Afghans know that once the Western troops leave, they are going to have to choose sides — the Kabul government or the Taliban — and the Kabul government has little respect or credibility,” he told AFP.

Nato has tried to play down the importance of the attacks, pointing out that they are carried out by a tiny proportion of the Afghan forces that work with the International Security Assistance Force.

But US Defence Secretary Leon Panetta has acknowledged that he is “very concerned” about the attacks and the impact they are having on cooperation with Afghan allies.

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

Abdullah 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 United States.

“Sometimes you don't know who he calls the enemy — the Taliban or the Americans,” Abdullah told AFP.