A U.S. service member was killed in an apparent insider attack by Afghan forces in the east of the country late Saturday. A civilian contractor with NATO and at least two Afghan soldiers also died in the attack, according to a coalition statement and Afghan provincial officials. The nationality of the civilian was not disclosed.
The suspected insider threat attack occurred in Wardak Province.
A U.S. official, speaking on condition of anonymity, confirmed the nationality of the NATO service member killed was American.
The toll has climbed steadily in recent months with a spate of attacks by Afghan army and police against American and NATO troops, and questions about whether allied countries will achieve their aim of helping the Afghan government and its forces stand on their own after most foreign troops depart in little more than two years.
Attacks by Afghan soldiers or police - or insurgents disguised in their uniforms - have killed 52 American and other NATO troops so far this year.
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The so-called insider attacks are considered one of the most serious threats to the U.S. exit strategy from the country. In its latest incarnation that strategy has focused on training Afghan forces to take over security nationwide - allowing most foreign troops to go home by the end of 2014.
Although Obama has pledged that most U.S. combat troops will leave by the end of 2014, American, NATO and allied troops are still dying in Afghanistan at a rate of one a day.
Even with 33,000 American troops back home, the U.S.-led coalition will still have 108,000 troops - including 68,000 from the U.S. - fighting in Afghanistan at the end of this year. Many of those will be training the Afghan National Security Forces that are to replace them.
"There is a challenge for the administration," O'Hanlon said, "to remind people in the face of such bad news why this campaign requires more perseverance."