Insurgents on Monday attacked the military side of Kabul's international airport, which houses a NATO headquarters, and explosions and gunfire were occurring, Afghan army and police said.
The airport was closed to all civilian air traffic because of the attack, an airport official said.
The Kabul police said in an announcement that attackers wearing suicide vests had occupied a tall building on the west side of the airport and were firing at the military facility.
A statement said there was at least one large explosion at around 4:30am and a gun battle began with security forces.
"We closed the Kabul airport runway so that civilian aircraft don't get hit by bullets. They are in a high building that they are shooting from," said Yaqub Rassouli, the civilian chief of Kabul airport.
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Afghan army General Murad Ali Murad said police and military forces were exchanging gunfire with insurgents.
"Outside the airport, in the civilian area, there is a tall building under construction and they are shooting at the military side from there. The building is surrounded and there is sporadic shooting. Not enough to damage the military side. We don't know how many terrorist bombers are in there," he said.
A series of explosion were heard from the direction of the airport and residents heard what sounded like a dozen explosions coming from the direction of the military's facilities. They said the explosions sounded like rocket-propelled grenades along with automatic weapons fire. The explosions could be heard in downtown Kabul, a few kilometres (miles) away from the airport, located on the outskirts of the capital.
The US-led NATO coalition's Joint Command headquarters at the airport runs the day-to-day operations of the nearly 12-year-old war against insurgents. The airport's military side is also used for NATO transport and other aircraft.
"It started just after dawn prayers and I counted about a dozen explosions, mostly RPG fire, coming from the airport," said Emayatullah, who lives next to the airport. Like many Afghans he uses only one name.
The International Assistance Force's Joint Command said it was aware of reports of an attack, but had no further details.