This year, U.S. troops in Afghanistan are dying at a rate of one per day thanks in part to the dramatic escalation of Afghan security forces turning their weapons on U.S. allies in so-called green-on-blue attacks. Today, as CBS News' Tucker Reals reports, two U.S. troops were killed when an Afghan Local Police officer shot at them in the western Afghan province of Farah. Last Friday, two more green-on-blue attacks left six American troops dead. Just this year, Afghan security forces have turned their guns on NATO allies 31 times resulting in the deaths of at least 39 coalition forces. Is there a way to explain these attacks?

Taliban infiltration of the police Just yesterday, the head of the Afghan Taliban Mullah Omar spun the latest attacks as evidence of a widespread Taliban infestation of Afghan law enforcement. "Thanks to the infiltration of the Mujahideen (holy warriors), they are able to (safely) enter bases, offices and intelligence centers of the enemy," he said in a statement marking the Islamic holiday of Eid al Fitr. "Then, they easily carry out decisive and coordinated attacks, inflicting heavy losses on the enemy." But the Pentagon rejects this explanation.

Lone gunmen Though the Taliban repeatedly claim responsibility for green-on-blue attacks, U.S. officials says that's typically not the case. "The U.S. Defense Department maintains the attacks are generally not carried out by insurgents, but rather individual members of the Afghan security forces who may develop a grudge against their Western allies," writes CBS News' Reals. "Defense Secretary Leon Panetta announced earlier this week that new counter-intelligence measures had been adopted during the past year to try and prevent the green-on-blue attacks. While he acknowledged that some of the incidents have been connected to insurgent groups, he insisted that the vast majority of the attacks appear to be carried out by people with no known links to, or coordination with, the Taliban or other militant organizations."

Stress and fatigue NATO has also tried to dispel the claim that Taliban insurgents are carrying out the attacks, blaming them to fatigue and petty personnel matters. “So when we talk about the insider threat or some call them again green on blue incidents, we talk about 27 incidents so far in this year and we had 37 people killed in those incidents… And most of these incidents were caused by personal grievances, by stress situation, or by battle fatigue,” said NATO spokesman Brig. Gen. Gunter Katz. He also downplayed the number of green-on-blue attacks given the six of NATO's footprint. “Yes we had 27 very tragic incidents. We take them very very seriously," he said. "But we must not forget that on the other side we still got almost 500,000 soldiers and policemen who work together, as we speak right now actually, in order to crush the insurgency and fight for more stability and security here in this country.”

Insufficient vetting Another reason cited for the uptick in attacks is insufficient vetting of recruits for the Afghan security forces. It's an issue Army Gen. Martin Dempsey spoke to in Bogota Colombia. "Dempsey said NATO will have to build up the Afghan counterintelligence function to stop Taliban members from infiltrating the Afghan army or police to kill NATO and allied personnel," reports Jim Garamone. Ultimately, Dempsey said that it will be up to the Afghans to get serious about the vetting process. “There’s an eight-step vetting process that includes everything from letters from tribal leaders to biometrics,” he said. “But where this will finally be solved is when they have the same vetting as we do, because they know who they are better than we do. And the same was true in Iraq.”