Story highlights The attacker is also killed

The Americans were contractors

Kabul, Afghanistan (CNN) The Afghan Taliban have claimed responsibility for a suicide attack that killed 3 American contractors at a military base attached to the Kabul airport.

The attacker in the Thursday incident was a Taliban agent who "had penetrated into the security forces and was waiting for such a target for a long time," a spokesman for the group, Zabiullah Mujahid, said Friday.

"Yesterday in the evening he managed to get to a crowd of invading and infidel American military forces where he turned his gun towards them and opened fire," he added. "During the gun battle, Ehsanullah was also killed by the enemy."

A U.S. military official earlier told CNN the three American were contractors, not active duty forces.