Afghan Local Police gather for a graduation ceremony in Farah province. Photo: ISAF

Rogue Afghan soldiers and police turning their weapons on their allies are now the leading cause of death for NATO troops. On Aug. 28 a man wearing an Afghan army uniform opened fire on Australian soldiers in the southern province of Uruzgan, killing three and wounding two.

That attack brought to 15 the total number of NATO personnel killed in so-called “green-on-blue” assaults in August — and raises serious doubts about the alliance’s war strategy, which calls for close cooperation between foreign and Afghan troops as the Afghans gradually assume responsibility for their own security.

Of the other 35 international troops who died in Afghanistan this month, 12 were killed by Improvised Explosive Devices and nine died in helicopter crashes. Insurgent gunfire and a suicide bomber accounted for the remaining fatalities.

Marine Corps Gen. John Allen, commander of NATO’s International Security Assistance Force, told Danger Room he didn’t know why the Afghan troops turned their weapons on their foreign allies. He implied the “sacrifices associated with fasting” during the the Muslim holy month of Ramadan might have played a role — then quickly qualified the remark, saying Ramadan wasn’t exclusively the problem. In any event, “there is an erosion of trust that has emerged from this,” Allen said in a separate interview.

For its part, the Afghan government blames “infiltration by foreign spy agencies.” Allen said he looked forward to seeing proof of this assertion. Along with the green-on-blue attacks, there has also been a spike in Afghan troops killing other Afghan troops. “They’re suffering casualties from the same trend that we’re suffering” from, said Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff.

“Were the attacks the result of some kind of Taliban infiltration, the problem would thus be one of counter-intelligence,” explained Andrew Exum, an expert on low-intensity warfare. “The alternative — that relations between Afghan forces and their Western partners have structurally deteriorated in fundamental ways — is a far tougher problem to address.”

During Danger Room’s January visit to remote Paktika province in eastern Afghanistan, the rising tension between U.S. and Afghan forces was evident. When an Afghan police recruit began behaving erratically and overstepping his authority, his American trainers took no chances. They fired him — but only after carefully disarming him.

The reasons for the insider attacks are unclear. But the trend of more and more such assaults is inarguable. Before August, green-on-blue attacks accounted for just 12 percent of NATO troops killed. In 2011 they amounted to just six percent — up from three percent in 2010. Foreign soldiers wounded in green-on-blue incidents have also increased steadily in the past three years.

August’s insider killings occurred in 18 of Afghanistan’s 34 provinces but are concentrated in the southern and eastern battlegrounds, according to an analysis by Long War Journal. The three southern provinces of Helmand, Kandahar and Uruzgan account for the majority of green-on-blue attacks.

In the face of the rapidly-escalating insider threat, Allen, who is due to be replaced soon as ISAF’s top general, has not signaled any change in NATO’s strategy. Foreign troops will continue working closely with the Afghan soldiers who now represent statistically the biggest danger to their lives.

In fact, NATO troops should work more closely with Afghan, Exum advised. “I urge U.S. and allied troops in Afghanistan to remember that the only people who can truly protect them from green-on-blue violence are the Afghans themselves.”

The international alliance is scrambling to mitigate the threat. It’s now policy for at least one NATO soldier — a “guardian angel” — to watch over any gathering of Afghan and alliance troops, weapon loaded, “and hopefully identify people that would be involved in those attacks,” Defense Secretary Leon Panetta said.

But Panetta himself said spotting attackers before they pull the trigger could prove difficult. “It’s clear that there’s no one source that is producing these attacks.”