NATO says an explosion inside Bagram Airfield, a large U.S. base north of Kabul, has caused casualties.

The statement issued by Operation Resolute Support says the blast happened early Saturday and that "force protection and medical teams are responding to the situation," without providing further details.

The Taliban have fired rockets at Bagram in the past. Afghan officials confirm reports of the explosion but could not provide further details because they do not have access to the base.