U.S. Defense Secretary Ash Carter has announced today that four Americans were killed by an explosion inside Bagram, an airbase just north of Kabul. Two members of the armed services and two contractors have died in Bagram. Another 16 Americans and one Polish soldier are among those inured.

The Taliban has taken credit for the suicide attack.

Despite being targeted by terrorists in the past, this marks the first time Bagram, America’s largest military facility in Afghanistan, has been attacked within the base – marking a huge breach in security.

The attack took place this morning. The man had posed as an Afghan laborer reporting for duty when he proceeded to detonate the explosive in his vest.

Secretary Carter is “deeply saddened” by the loss and announced an investigation is underway.