Fourteen airmen who helped secure a U.S. complex that hosts inter-continental ballistic missiles have been suspended from their duties due to an investigation into "illegal drug activity," the U.S. military said on Friday.

"The drug allegations involving these 14 airmen are credible," said Air Force General Robin Rand, Commander of Air Force Global Strike Command, adding the allegations involved activities by the junior airmen during their off-duty hours.

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Rand, speaking to reporters, declined to specify which drugs were involved.