An explosion at a US airfield in Afghanistan early Saturday killed four Americans—two service members and two contractors, CNN reports. Another 16 US service members and a Polish soldier were injured in the apparent suicide attack inside Bagram Air Field. According to the AP, a statement from NATO's Resolute Support mission said the blast happened around 5.30am and that "force protection and medical teams are responding to the situation." US Defense Secretary Ash Carter says he's "deeply saddened" by the attack.
The Taliban claimed responsibility for the attack, which they said was carried out by a suicide bomber inside the base. Zabihullah Mujahid, a spokesperson for the insurgent group, said the attack had been planned for four months. The Taliban says it targeted "a sports ground where...important people and soldiers were busy exercising." It appears people on the base were gathering for a run when the explosion happened. A spokesperson for the governor of Parwan province, where the air field is based, says laborers employed at Bagram line up at the gates around dawn and an attacker could have been among them on Saturday. (Read more Afghanistan stories.)