Today's attack in the east of the country appears to be the latest in a series of insider attacks on foreign forces. The NATO-led coalition said more information would be released later after an investigation into what happened.
Insider attacks in the past have been claimed by Taliban insurgents as proof they can infiltrate Afghanistan's Western-trained security forces. Other cases have involved personal disputes between Afghan forces and their trainers.
The Taliban earlier today issued a statement claiming that a "battle" between Afghan forces and foreign trainers had resulted in several deaths and injuries, but Afghan government officials contacted at the time could not confirm any such incident.