An American drone apparently killed two U.S. troops in Afghanistan last week in what may be a first-of-its-kind case of friendly fire.

NBC's Jim Miklaszewski writes that the strike killed a Marine Staff Sergeant and Navy corpsman while they were reinforcing Marines under fire from the Taliban in Helmand Province, Afghanistan. The Marines reportedly saw the troops headed towards them through a Predator's infrared camera, could not distinguish them from attacking Taliban and ordered in the Predator-borne Hellfire missile airstrike that killed the two men.

"It's believed that this is the first time that U.S. service members have been killed by a Predator in a friendly fire incident," Miklaszewski reports.

The strike follows the Los Angeles Times' in-depth chronicling of a February 2010 drone strike gone awry. In the incident, a combination of misinterpreted signals and the fog of war led drone operators and special operations forces on the ground to think a convoy of Afghan civilians in vehicles was an inbound Taliban attack force. (Read the transcript of the chatter between the drone pilots and the ground troops here.) The strike killed 15-16 men, one woman and three children according to the U.S. military. Local Afghans set the number of dead at 23, including two children.

Drone strikes and the accidental civilian casualties they cause have been the subject of intense debate over the years as the U.S. has increasingly relied on unmanned aerial systems in Afghanistan and Pakistan. This latest incident, apparently the first friendly fire incident against U.S. forces involving an unmanned system, and the investigation that will follows adds new fuel to the debate over the reliance on unmanned systems and their precision in combat.

Photo: Flickr/U.S. Air Force

Adam Rawnsley is a former think-tanker and contributor to Danger Room who writes about terrorists, pirates and associated bad guys.