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U.S. and NATO troops in Afghanistan are being ordered to carry loaded weapons at all times while on base, in response to a rash of Afghan soldiers and policemen turning their weapons on coalition forces.

The directive, confirmed by Fox News, was issued by International Security Assistance Force Commander Gen. John Allen. It says that troops should no longer simply keep ammunition magazines close by -- instead, those magazines should be loaded in the weapons.

Depending on where troops are stationed in Afghanistan, this is not an entirely new practice. At Bagram Air Base, for example, weapons carried by NATO troops are often inspected upon entry to make sure they are loaded. But that was not the practice at ISAF headquarters in Kabul where service members have, until now, been directed to empty their ammunition upon entering the base.

The directive comes as military officials scramble to find ways to fight the so-called "green-on-blue attacks" or "insider threats," as Defense Secretary Leon Panetta characterized it this week.

"Make no mistake about it -- I've been very concerned about these incidents because of the lives lost and because of the potential damage to our partnership efforts," Panetta said at a Pentagon briefing Tuesday.

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    Panetta said ISAF is taking other steps, too, including increased counterintelligence efforts, a new eight-step vetting process for new recruits, and new NATO training requirements.

    Two Americans were killed Friday when a local village policeman opened fire in Farah province in the west. Two more Americans were shot and wounded in a separate incident in the southern province of Kandahar.

    Thirty-nine NATO service members, mostly Americans, have been killed in these types of attacks so far this year. In one horrifying scene earlier this year, an Afghan soldier shot and killed an American while he was playing volleyball on base.

    The attacks are up significantly -- from 11 deaths in 2011. There were four such deaths in all of 2007 and 2008.

    Panetta largely blamed the trend on Taliban influence and self-radicalization. But he conceded that the problem is not that simple.

    Terry Walker, a former Marine trainer in Helmand Province, told Fox News that most of these incidents are due to personal and cultural conflicts. He said Afghans simply have a different way of dealing with their problems.

    "You have a strong influence that's tribal," Walker said. "Afghans can't be insulted and they have no conflict resolution capability. The smallest thing can set them off."

    Sometimes it's not so small. One military official detailed an incident where an Afghan man was being repeatedly raped by fellow Afghans in his police unit. When a British service member teased the man about the abuse, the Afghan man "snapped" and killed him.