A friendly fire air strike in Afghanistan's Zabul Province killed five U.S. special operations soldiers and at least one Afghan soldier last night.

Coalition troops were conducting a security operation in preparation for Saturday's runoff presidential election when they were ambushed by Taliban forces. The soldiers called in air support, and the aircraft accidentally hit the U.S. troops' position, according to Zabul police chief Ghulam Sakhi Roghliwanai.

The coalition said in a statement:

"The casualties occurred during a security operation when their unit came into contact with enemy forces. Tragically, there is the possibility that fratricide may have been involved. The incident is under investigation. Our thoughts are with the families of those killed during this difficult time."

As the New York Times points out, the incident, if confirmed, would be among the deadliest instances of U.S. friendly fire since the war in Afghanistan began in 2001.

[Image via AP]