An unspecified number of American and Afghan troops were killed by an Afghani in uniform who opened fire on Monday in the eastern province of Wardak.
Fox News reported two American servicemen, likely members of an elite special operations unit, were killed.
The Wall Street Journal said there were "multiple casualties," and they included U.S. troops, Afghan service members and the police chief for Jalrez district.
The Associated Press reported an Afghan police officer stood up in the back of a police pickup truck, grabbed hold of a machine gun and started firing at U.S. special operations forces and Afghan police in the police compound.
The fatalities come one day after Afghanistan President Hamid Karzai accused the United States of working with the Taliban to extend America's military mission past 2014.
They also come as Secretary of Defense Chuck Hagel just wrapped his first official talks with Mr. Karzai.
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