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Afghan duplicity has cost the lives of six American troops over the past week and betrayed the trust that's an essential element in the international coalition's formula for winding down the decade-long war.

In a conflict where the enemy wears no uniform, it takes trust to work side by side with Afghans whose loyalties are hard to decipher and who sometimes turn out to be Taliban sympathizers.

It is difficult to gauge what it will take to rebuild a bond of trust after repeated instances of Afghan soldiers and civilians, or civilians posing as soldiers, turning their guns on American and other allied troops. At some point, it calls into question the viability of a military strategy that requires close teamwork with Afghan troops, although the Obama administration is adamant that it will stay the course in Afghanistan.

Six U.S. troops have been killed in Afghanistan since Feb. 1 by their supposed Afghan allies, compared with two in combat with the Taliban, according to an Associated Press review of casualty data through Friday. Combat deaths typically are lower in the off-peak winter fighting season.

"There is something fundamentally wrong here," says Peter Mansoor, a retired Army colonel who was Gen. David Petraeus' executive officer in Baghdad in 2007-08. He said Iraqi troops sometimes betrayed their U.S. partners but not nearly to the extent seen recently in Afghanistan.

Administration officials insist there will be no backing away from working hand in hand with Afghan forces.

"Let me make clear: We will not be intimidated by what the enemy does," Defense Secretary Leon Panetta told soldiers of the 101st Airborne Division while visiting Fort Campbell, Ky., on Friday. "We will not change the course we are on to achieve the mission in Afghanistan."

He was referring to a strategy, first endorsed by Washington's NATO partners in November 2010 and expected to be reaffirmed in May at a NATO summit meeting in Chicago, that calls for gradually handing over responsibility for security to the Afghan army and police by the end of 2014. Panetta has said he hopes Afghans will assume the lead combat role across the country by mid-2013, with U.S. and other NATO troops remaining in smaller numbers to perform numerous support missions.

To get there, U.S. and allied troops are not only continuing to train Afghan forces but also are increasingly partnering with them in the field, putting their lives in each other's hands.

This is where the trust factor counts the most.

Mark R. Jacobson, the deputy NATO senior civilian representative in Afghanistan until last summer, says he is optimistic that trust can be rebuilt and he believes the basic U.S. approach remains sound. But he is troubled by what he sees as the Taliban's successes in exploiting Afghan outrage over the U.S. military's mistaken burning of Qurans and by Taliban infiltration of Afghan security forces.

"They are deliberately seeking to make you mistrust that person standing next to you," Jacobson said in an interview. He is now a senior fellow at the German Marshall Fund of the United States, a think tank.

It's part of a calculated campaign by the Taliban, he said, to drive a "psychological wedge" between Afghan government forces and their foreign partners and thereby cripple a key element of the war strategy.

"If we can't train the Afghan national army appropriately, we're never going to be able to leave and we're never going to win," Jacobson said.

It's not just American troops who are getting killed by their supposed Afghan partners. Four French troops were gunned down by a rogue Afghan soldier on Jan. 20. Paris responded by immediately speeding up its planned withdrawal of combat troops. An Albanian soldier was killed in an attack by Afghan police on Feb. 20.

There has been no heightened clamor on Capitol Hill to withdraw from Afghanistan, but Rep. Frank Wolf, R-Va., has renewed his call for the White House to assemble a panel of outside experts to review U.S. strategy.

"Congress and the Obama administration need to wake up and realize that things are not going well in Afghanistan, and it has nothing to do with the capabilities of our troops," Wolf said on the House floor Thursday. It has to do with "Afghan security forces gunning down their American advisers," he said.

Wolf also is worried by the persistent problem of Taliban havens on the Pakistan side of the border.

Navy Adm. James Stavridis, the top NATO commander, said he sees no need to change course in Afghanistan.

"As I look at the broad sweep of our strategy there, I am convinced that we should continue with transitioning Afghanistan's security to the Afghans," he told a Senate panel Thursday. He called himself "cautiously optimistic" that the plan now in place ultimately will succeed in stabilizing the country.

In a separate appearance before Congress, Gen. Ray Odierno, the Army chief of staff and former top U.S. commander in Iraq, framed the problem diplomatically by saying only a tiny fraction of Afghan security forces are targeting Americans. He applauded U.S. troops for their restraint in the face of treachery.

"I know it's very difficult for (U.S. soldiers) when we have somebody who is working hard, dedicating themselves to the mission in Afghanistan and somebody who they're helping comes behind and kills them," he said.

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Online:

NATO: http://www.nato.int/cps/en/natolive/topics_69349.htm

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Robert Burns can be followed on Twitter at http://www.twitter.com/robertburnsAP