The U.S. Air Force says three poorly trained airmen caused $1.8 million in damage to one of its nuclear missiles in 2014 while they were conducting routine maintenance on the weapon.

The incident involving a Minuteman III intercontinental ballistic missile occurred at a remote air base in the western state of Colorado, but came to light only Friday as the Air Force released a report with some details of the accident.

FILE - U.S. Air Force technicians perform an elect FILE - U.S. Air Force technicians perform an electrical check on an LGM-30F Minuteman III intercontinental ballistic missile in its silo at Whiteman Air Force Base, Missouri. FILE - U.S. Air Force technicians perform an electrical check on an LGM-30F Minuteman III intercontinental ballistic missile in its silo at Whiteman Air Force Base, Missouri.

The Air Force said the accident caused no injuries and did not pose a public safety risk. The airmen were stripped of their clearances to work on the nuclear missile for a lengthy period of time, but since then they have been retrained and returned to their jobs.

The Air Force report of the incident said that the missile "became non-operational" during a diagnostic test on May 16, 2014, and that a "mishap crew" chief investigating why the next day "did not correctly adhere to technical guidance ... subsequently damaging the missile."

The Air Force did not release further information about the incident, many details of which remain classified. But it said there was "clear and convincing evidence" of what caused the accident.

It said the mishap crew chief did not follow technical guidance in investigating why the missile was not working correctly and "lacked the necessary proficiency level" to anticipate what might go wrong while working on it.

The Air Force said it had modified its training as a result of the incident and alerted other units that operate Minuteman III missiles about the circumstances that led to the Colorado accident.