Four US Air Force officers have been relieved of command after nuclear missiles were mistakenly flown between two bases in the United States.Three colonels and a lieutenant colonel were removed from their posts while about 65 Air Force members had their permission to handle nuclear weapons withdrawn as a result of the incident, which took place in late August, officials said.Six cruise missiles armed with nuclear warheads were taken out of shelters at Minot Air Force Base in North Dakota and loaded onto one wing of a B-52 bomber.Six further missiles which were not armed with nuclear warheads were loaded onto the other wing of the aircraft.The USAF acknowledged the security level was "not up to the standards that we would have liked" for nuclear arms, but stressed that the case was an isolated incident and that the procedures for handling nuclear weapons were sound.The B-52 was meant to ferry only cruise missiles without nuclear warheads as part of a programme to consolidate weapons for decommissioning.© Independent Television News Limited 2007. All rights reserved.