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An Air Force unit responsible for dozens of nuclear missiles failed a recent safety and security inspection -- a setback that comes just months after the Air Force temporarily sidelined 17 officers in connection with a prior inspection flop.

The latest failure was recorded by the 341st Missile Wing at Malmstrom Air Force Base, Mont. According to Air Force Global Strike Command, the unit received an "unsatisfactory" rating during the inspection in early August after personnel made "tactical-level errors" during an exercise.

"This failure resulted in the entire inspection being graded 'unsatisfactory,'" a statement from Global Strike Command said.

Commander Lt. Gen. Jim Kowalski stressed in the statement that the failure does not mean the safety of America's nuclear arsenal is at risk, and that the inspections are "designed to be tough."

But the failure comes on top of other disappointing news for the Air Force's nuclear weapons force.

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Last spring the 91st Missile Wing at Minot Air Force Base, N.D., received weak grades on an inspection but did not fail it outright; that performance was so poor, however, that 17 officers temporarily lost their authority to operate missiles.

The group's deputy commander said at the time it was suffering "rot" within its ranks.

"We are, in fact, in a crisis right now," the commander, Lt. Col. Jay Folds, wrote in an internal email.

The unit in Montana that was the focus of the latest inspection is responsible for 150 Minuteman 3 nuclear missiles that stand on 24/7 alert for potential launch against targets around the globe.

Kowalski, who spoke with the Associated Press, would not discuss details of the failure or explain the exercise, citing security, except to say that it did not involve the crews who monitor the missiles from inside underground launch control capsules. That left open the possibility that it involved airmen responsible for security, weapons maintenance or other aspects of the highly sensitive mission.

"This unit fumbled on this exercise," Kowalski told the AP by telephone from his headquarters at Barksdale Air Force Base, La.

The Associated Press contributed to this report.