Large explosions are being heard coming from the military side of Kabul international airport, which houses a NATO headquarters.
The explosions began about 4:30 a.m. Monday from the direction of the military headquarters.
The U.S.-led NATO coalition's Joint Command headquarters at the airport runs the day-to-day operations of the nearly 12-year-old war against an insurgency in Afghanistan. The airport's military side is also used for NATO transport and other aircraft.
The cause of the explosions was not immediately clear, but insurgents usually carry out attacks in the early morning.