Kabul, Afghanistan (CNN) -- A coalition service member and a civilian contractor were killed Saturday in an attack believed to involve an Afghan soldier, officials said, in what appears to be the latest incident of local forces turning their weapons on NATO troops.
More that 50 coalition troops have been killed in so-called "insider" or "green-on-blue" attacks this year, raising concerns about the stability of Afghan security forces ahead of planned U.S. and NATO withdrawals by the end of 2014.
The service member and the contractor were killed in eastern Afghanistan, according to an ISAF statement.
There were also a number of Afghan National Army casualties, the coalition said.
ISAF did not immediately release details about the attack, the suspected attacker or the nationality of the casualties.
A joint Afghan National Army and ISAF investigation is under way, the statement said.
"Green-on-blue" refers to a color coding system used by the military, in which blue refers to the friendly force, in this case ISAF; and green refers to allied friendly forces, in this case Afghan National Security Forces.
