US and allied officials have said they had intelligence that suicide bombers were threatening to attack the airport. The Pentagon confirmed the blast, with no immediate word on casualties.
"We can confirm an explosion outside Kabul airport. Casualties are unclear at this time. We will provide additional details when we can," said Pentagon Spokesman John Kirby.
"We can confirm that explosion at Abbey Gate was result of a complex attack that resulted in a number of US & civilian casualties. We can also confirm at least one other explosion at or near Baron Hotel, a short distance from Abbey Gate," Kirby said.
Russia's Foreign Ministry says a second explosion has gone off outside Kabul airport. The twin suicide attacks killed at least 13 people and wounded another 15.