A suicide bomber attacked the largest U.S. base in Afghanistan early Saturday morning, killing at least four and injuring 14 others, the U.S. military said. The Taliban claimed responsibility for the attack.

Defense Secretary Ash Carter issued a statement saying two of the victims were U.S. servicemembers and the other two were U.S. contractors. Sixteen other U.S. servicemembers were wounded, he said, in addition to a Polish soldier working with NATO. The attacker reportedly came on Bagram Air base around 530 a.m. posing as a local worker.

In a statement, the Taliban said a suicide bomber had targeted "a sports ground where more than 100 military officers, important people and soldiers were busy exercising," CNN reported. A defense official told the Daily Beast that the attacker targeted a group gathered after a run. It was the deadliest attack in Afghanistan since December 2015 when a suicide bomber detonated himself just outside Bagram, killing six U.S. airmen.

"To the family and friends of those who lost their lives today, we share your loss and our thoughts are with you. We offer you our deepest condolences. For the family and friends of those wounded in today’s attack, let me assure you they are receiving the best care possible, and we will keep them in our thoughts today,” said U.S. Army Gen. John W. Nicholson, commander of the mission there. The Taliban has ramped up attacks around the country in what has increasingly become a worsening security situation. On Thursday, at least four people were killed and another 120 were injured after a suicide bomber drove a lorry loaded with explosives into the German consulate in the northern city of Mazar-e Sharif. And earlier this month, in the northern city of Kunduz, two U.S. troops during a raid to capture a Taliban; another 30, including civilians, were killed in a US airstrike launched during the attack. And Bagram, now in lockdown, frequently comes under mortar fire. There are roughly 10,000 U.S. troops in Afghanistan.

-- Nancy Youssef