NATO says three members of the Afghan national security forces have been killed in an attack at Bagram Air Field, a sprawling U.S. base north of Kabul.

The coalition said Tuesday it has not yet confirmed whether the three were killed by rockets or mortar rounds that were fired at the base around late Monday night.

Gen. Akram Begzad, the police chief in Parwan province where the base is located, said a rocket was fired at the base from an undisclosed location. He says two Afghan intelligence employees were among those killed in the attack.

Militants occasionally fire mortars or rockets at Bagram, but the attacks generally cause little or no damage.