A Taliban suicide bomber detonated himself on Tuesday outside Kabul International Airport, killing three foreign advisers and an Afghan interpreter, police said.
The nationalities of the foreign advisers were not immediately clear.
The explosion comes days after one of the most audacious militant attacks in a year on the airport, which is used by both civilians and the military.
A Taliban spokesman, Zabihulllah Mujahid, claimed responsibility for Tuesday's attack. "In this successful attack up to 15 invader soldiers were killed or wounded and many vehicles were damaged," he added.
Kabul airport is home to a major operational base for NATO-led forces that have been fighting the Taliban for 12 years. Security includes soldiers and police, guard towers and checkpoints.
Militants often fire rockets into the airport, causing little damage, but frontal attacks on the heavily guarded facility are rare and represent an ambitious target for insurgents.