WASHINGTON (AP) — An Air Force unit that operates one-third of the nation’s land-based nuclear missiles has failed a safety and security inspection, marking the second major setback this year for a force charged with the military’s most sensitive mission, the general in charge of the nuclear air force told The Associated Press on Tuesday.

Lt. Gen. James M. Kowalski, commander of Air Force Global Strike Command, said a team of “relatively low-ranking” airmen failed one exercise as part of a broader inspection, which began last week and ended Tuesday. He said that for security reasons he could not be specific about the team or the exercise.