KABUL, Afghanistan (AP) — A U.S. Air Force C-130J military transport plane crashed overnight at an air base in eastern Afghanistan, killing six American airmen and five civilians on the aircraft, the U.S. military said Friday.

The crash happened shortly after midnight Thursday at Jalalabad air field, 125 kilometers (80 miles) from the capital, Kabul, said U.S. Air Force Maj. Tony Wickman, spokesman for the 455th Air Expeditionary Wing.

An unknown number of people on the ground were also killed, he said, without elaborating. Afghan officials had no immediate details on the crash or any casualty figures.

The six U.S. service members who died comprised the plane’s crew. The passengers were civilian contractors working with NATO’s Resolute Support mission and were the only passengers on board, Wickman added.

The airmen were assigned to the 774th Expeditionary Air Lift Squadron, part of the 455th, and the plane, a Super Hercules, crashed “shortly after take-off wholly within the airfield,” he said.

President Barack and Michelle Obama extended condolences to the American and Afghan families who lost relatives in the crash.

In a statement, he said: “As we mark this terrible loss of life, we are reminded of the sacrifice brave Americans and our Afghan partners make each and every day in the name of freedom and security.”

The Taliban claimed they shot the plane out of the sky, but the group is prone to exaggeration.

Wickman dismissed the claim, saying that “it is with high confidence that we can say it does not appear that enemy fire was involved.” Few other details were available and an investigation was underway, he added.

There are about 1,000 coalition forces in eastern Afghanistan, including U.S. and Polish forces, as well as about 40,000 Afghan troops, according to NATO.

There are also up to 35,000 civilian contractors across the country.

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Associated Press writer Lolita C. Baldor in Washington contributed to this report.