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JALALABAD, Afghanistan — Six U.S. airmen were among 13 people killed early Friday when an American C-130 transport plane crashed while taking off in Afghanistan, a U.S. military official said.

The incident occurred shortly after midnight local time (3:19 p.m. ET) at Jalalabad airfield, coalition spokesman U.S. Army Col. Brian Tribus said.

Tajawar Khan, 58, who works as a caretaker near the base, said he witnessed a "huge explosion and massive fire" after hearing a "strange sound" from a plane. Khan added that the blaze raged for several hours.

Six of the dead were U.S. crew members aboard the aircraft. The other victims were five civilian contractors, who were passengers, and two Afghan civilians who were killed on the ground, Tribus added.

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A military statement confirmed Friday that four of the airmen were deployed from Dyess Air Force Base in Texas, while two others were deployed from Hanscom Air Force Base in Massachusetts.

The contractors' nationalities were not immediately released.

U.S. Air Force Maj. Tony Wickman, spokesman for the 455th Air Expeditionary Wing, told The Associated Press the the Super Hercules aircraft crashed "shortly after take-off wholly within the airfield."

The civilian contractors were working with "Resolute Support," the NATO-led mission to train and advise Afghan security forces. It follows the military mission in Afghanistan after combat operations ended at the end of 2014.

The cause of the crash has not been determined.

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."

The C-130 is a four-engine turboprop aircraft used to transport personnel and oversized cargo.