The International Security Assistance Force said five of its servicemen died Monday during a security operation in southern Afghanistan when their unit came in contact with enemy forces.
"Tragically, there is the possibility that fratricide may have been involved," ISAF said in a statement. "The incident is under investigation."
Defense and military officials told NBC News that the soldiers were members of U.S. special forces working with the Afghan military.
The American and Afghan troops were conducting security sweeps on polling sites ahead of this weekend's run-off for the Afghan presidential election when they came under attack from Taliban forces, the officials explained.
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