According to Al Jazeera, a police source revealed that fighting broke out just outside Herat city, and the attacker who fired on ISAF civilian contractors was killed following the incident.
NATO and official Afghan reports offered conflicting accounts of the shooting; NATO spokesman Maj. Adam Wojack said an assailant wearing an Afghan army uniform was killed, with another attacker fleeing the scene.
"Two NATO helicopters have arrived on the scene to try and quell what seems to have been some fighting that has broken out," Al Jazeera's Bernard Smith reports.
So-called "green-on-blue attacks," referring to Afghan forces turning on NATO counterparts, have seen a spike in 2012, following the burning of Qurans at U.S. air base in February and American Staff Sergeant Robert Bales allegedly shooting and killing 16 Afghan civilians in March.
The Associated Press has confirmed the report, noting that 26 soldiers have been killed in 2012 in this type of attack.
More information on the latest attacks is set to be released Monday.