The attacker entered on foot hidden among a group of workers reporting for duty at Bagram Air Base early in the morning, said Abdul Wahid Sediqi, spokesman for the governor of Parwan Province, where the military base and airfield are. Once inside the base, the attacker detonated explosives, Mr. Sediqi said.- New York Times

Here is Secretary of Defense Ash Carter’s statement:

I am deeply saddened to learn that an explosion early this morning at Bagram Airfield in Afghanistan has resulted in U.S. casualties. An apparent suicide bomber has taken the lives of two U.S. service members and two U.S. contractors working on the base. The explosion wounded 16 other U.S. service members and one Polish soldier participating in our NATO mission. I want to express my sincere condolences to the families of the fallen, and I want to reassure the loved ones of those injured that they are getting the best possible care. Force protection is always a top priority for us in Afghanistan, and we will investigate this tragedy to determine any steps we can take to improve it. For those who carried out this attack, my message is simple. We will not be deterred in our mission to protect our homeland and help Afghanistan secure its own future.

Image courtesy of Reuters