Four Americans dead in suicide bombing at Bagram Airfield in Afghanistan

KABUL, Afghanistan, Nov. 12 (UPI) -- A suicide bomber killed four Americans and injured 17 other people at a U.S. military base in Afghanistan on Saturday, the Defense Department said.

Two U.S. service members and two U.S. contractors were killed. An additional 16 U.S. service members and one Polish soldier were injured in the explosion at Bagram Airfield near Kabul. U.S. Secretary of Defense Ash Carter confirmed the incident in a statement.

"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," Carter said. "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."

The Taliban claimed responsibility for the attack in which the suicide bomber entered the large and heavily guarded base around 5:30 a.m. dressed as a day laborer, a foreign security source told The Wall Street Journal.

Upon entering the base the bomber stood in a line with Afghan laborers reporting for duty and detonated the explosives on his vest, the BBC reported.

Bagram Airfield is a home base to tens of thousands of contractors. Patrols near the base have been the target of multiple Taliban rocket attacks and a suicide bombing in December 2015, which killed six U.S. soldiers.

"To those who target coalition forces, [Afghan National Defense Security Forces], and Afghan civilians, Resolute Support and [U.S. Forces Afghanistan] will continue to pursue our Train, Advise and Assist mission to help our partners create a better Afghanistan," Resolute Support Cmdr. Gen. John W. Nicholson said in a press release.