Witnesses said the blast struck a group of soldiers waiting at a checkpoint outside the military wing of Kabul International Airport.

An Afghan soldier who witnessed the bombing told Reuters the assailant initially hit a convoy of German vehicles, but the explosives did not detonate, giving the soldiers time to warn the drivers that a suicide attack was taking place.

A spokesman for the German forces in Afghanistan confirmed that the bomber made an initial failed attempt on two vehicles carrying German troops, and later set off the blast near the airport gate.

It was not immediately clear who was behind the blast, though reports said Taliban militants were suspected.

An Afghan airport official said civilian flights to and from the airport continued as normal.

(compiled from agency reports)