Four Americans killed in air base explosion in Afghanistan: U.S. defense chief

Four Americans were killed early Saturday morning in an explosion at a U.S. military base in Afghanistan, U.S. Defense Secretary Ash Carter said.

"An apparent suicide bomber has taken the lives of two U.S. service members and two U.S. contractors working on the base," Carter said in a statement, adding that the explosion also wounded 16 other U.S. service members and one Polish soldier.

"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," he said.

Zabiullah Mujahid, a purported Taliban spokesman, claimed responsibility for the attack. He twitted that the attack was part of the insurgent's yearly rebel offensive.

The blast on Saturday morning took place at Bagram Airfield, a main U.S. military base in Afghanistan over the past 15 years, located some 50 km north of the Afghan capital of Kabul.

On Thursday night, four Afghan security forces and three militants were killed and more than 130 residents wounded in a Taliban suicide truck bombing and ensuing gunfight against German Consulate office in northern Mazar-e-Sharif city.

These attacks highlight the rising insecurity in Afghanistan after the conclusion of the NATO-led forces combat mission in late 2014 and withdrawal of major parts of combat troops, analysts said. Endit