WASHINGTON (CNN) -- A six-week probe into the mistaken flight of nuclear warheads across the country uncovered a "lackadaisical" attention to detail in day-to-day operations at the air bases involved in the incident, an Air Force official said Friday.
Air Force Col. Bruce Emig was stripped of his responsibilities, sources say.
The investigation found that "a limited number of airmen" at both locations failed to follow procedures, said Maj. Gen. Dick Newton, assistant deputy chief of staff for operations.
Four officers -- including three colonels -- have been relieved of duty in connection with the August 29 incident in which a B-52 bomber flew from Minot Air Force Base in North Dakota to Barksdale Air Force Base in Louisiana.
The plane unknowingly carried a payload of nuclear-tipped cruise missiles.
"Nothing like this has ever occurred," Newton said.
"Our extensive, six-week investigation found that this was an isolated incident and that the weapons never left the custody of airmen -- were never unsecured -- but clearly this incident is unacceptable to the people of the United States and to the United States Air Force."
The probe also found there was "an erosion of adherence to weapons-handling standards at Minot Air Force Base and at Barksdale Air Force Base," Newton said.
"We have acted quickly and decisively to rectify this," he added.
Relieved of duty were the Minot wing commander and maintenance crew commander, and the Barksdale operational group commander.
Minot's munitions squadron commander was relieved of duty shortly after the incident.
Newton didn't name any of the officers, but Col. Bruce Emig had been the commander of the 5th Bomb Wing at Minot.
A number of other personnel -- "under 100," Newton said, including the entire 5th Bomb Wing at Minot -- have lost their certification to handle sensitive weaponry.
The matter will be referred to an Air Force convening authority to find out whether there's enough evidence to bring charges or any other disciplinary action against any personnel, Newton said.
Air Force Secretary Michael Wynne called the incident "an unacceptable mistake and a clear deviation for our exacting standards." Watch Wynne talk about the breakdown in procedures »
"We are making all appropriate changes to ensure that this has a minimal chance of happening again, but we would really like to ensure that it never happens again," he said.
Wynne has convened a blue-ribbon panel to review all of the Air Force's security procedures and adherence to them. That panel is to report back on January 15.
The probe into the incident, which ended this week, lists five errors -- all of them procedural failures to check, verify and inspect, Newton said.
The investigation found that nuclear warheads were improperly handled and procedures were not followed as the missiles were moved from their storage facility, transferred to the bomber and loaded onto it, Newton said.
The bomber carried six nuclear warheads on air-launched cruise missiles, but the warheads should have been removed from the missiles before they were attached to the B-52.
A munitions crew at Barksdale followed proper procedure when the plane landed, discovering the error and reporting it up the chain of command, Newton said.
The weapons were secured in the hands of airmen at all times and had been stored properly at Minot, Newton said.
He called it a "lack of attention to detail, a lack of effective leadership and supervision."
"Airmen did not do their jobs ... that would have prevented this incident from occurring," he said. E-mail to a friend