At least one person has been killed and four injured in a suicide bomb attack on the international airport in the Afghan capital, Kabul.
The bomber blew himself up near the airport entrance
Authorities say the bomber blew himself up in a car at the entrance to the military section of the airport.
Foreign troops appeared to be the target of the attack, reports say.
A BBC correspondent who was at the airport describes the blast as huge. The explosion shook windows and rattled houses a good distance away, he says.
The explosion happened early on Friday close to the entrance of the airport, which has separate military and civilian sections.
Television pictures from the scene suggest it went off near the entrance used by the Nato-led international force.
"A car drove fast and blew up next to a crowd of people which included Afghan National Army soldiers," an eyewitness named Mansur told the Associated Press news agency.
Interior ministry spokesman Zamiray Bashiray told the BBC the attacker had driven at a military convoy of the Nato-led force and had actually hit it, but the convoy had left the area.
He said the detonation took place a little later and it was Afghan army troops who were caught up in the blast.
Mr Bashiray said he believed one Afghan soldier had been killed and four people injured - two of them civilians.
Afghan troops told a BBC reporter who went to the scene that one of their colleagues had indeed been killed and five wounded, one seriously.
The Afghan soldiers had been due to fly to Italy for training.
A BBC correspondent who happened to be on a plane ready for take-off at the time said the blast had shaken the aircraft.
"It was really, really loud," he said.
He said airport staff visible from the plane had thrown themselves on the ground in fear.
Nobody has claimed the attack so far.
There are more than 50,000 US and other coalition troops fighting with Afghan soldiers against Taleban militants in Afghanistan.