Kabul, Afghanistan (CNN) -- Two private security contractors in Afghanistan were killed by coalition forces who mistook them for insurgents, the NATO-led International Security Assistance Force said Saturday.
The incident happened Friday on a highway in the central province of Wardak, ISAF said.
A coalition patrol on the highway had just been fired at by insurgents in a location known as a hot spot for attacks, ISAF said. A vehicle then approached the coalition patrol at a high rate of speed with a man shooting out of the vehicle's windows.
"Perceiving the vehicle to be a threat, the gunner fired at the vehicle and killed two of the occupants," ISAF said.
Coalition forces learned afterwards that the two people killed were private security contractors, ISAF said. Their employer wasn't immediately known.
ISAF said the contractors were probably trying to return fire against the same insurgents who had just attacked the coalition vehicle, and they had increased their speed to "break contact."
Coalition forces are now looking into the incident, ISAF said.