The Air Force says maintenance errors by three airmen damaged a nuclear-armed missile in its launch silo, a mistake that cost them their nuclear certification and triggered an accident investigation.

The accident happened May 17, 2014, but the Air Force only explained the consequences Friday after questions by The Associated Press. It released a statement to the AP and a brief summary of the investigation results.

The Air Force said the accident didn't risk public safety. The damaged missile was removed from its silo. The launch site is operated by the 320th Missile Squadron of the 90th Missile Wing in a remote area of northeastern Colorado.

The Air Force refused to provide details of the accident, saying they are classified and too sensitive to make public.