The US Air Force has launched an investigation after a B-52 bomber flew across the US last week mistakenly loaded with nuclear-armed missiles.
The missiles were mounted on the wings of a B-52 bomber
It follows reports in the Army Times that five missiles were unaccounted for during the three-hour flight from North Dakota to Louisiana.
The air force said the cruise missiles were safe at all times.
Army Times said the missiles were to be decommissioned but were mistakenly mounted on the bomber's wings.
The W80-1 warhead has a yield of five to 150 kilotons, the paper said.
The flight took place on 30 August, from the Minot Air Force Base in North Dakota to the Barksdale Air Force Base, near Bossier City, in Louisiana.
Air force spokesman Lt Col Ed Thomas said although this was an "isolated incident", Air Combat Command had directed a "command-wide stand down to review process at all of our bases".
Col Thomas said a general had been appointed to investigate the incident and would report by 14 September.
"At no time was there a threat to public safety. It is important to note that munitions were safe, secure and under military control at all times," Col Thomas said.
"The air force takes its mission to safeguard weapons seriously. No effort will be spared to ensure that the matter is thoroughly and completely investigated."
Army Times quoted the colonel as saying the loading crew involved had been temporarily "decertified" pending retraining and the investigation.
A military official told AFP news agency that President George W Bush had been informed of the mix-up.
"There are procedures in place and they kicked in and worked," the official said.
The BBC's Adam Brookes in Washington says experts have made it clear that if the plane had crashed there would not have been a nuclear explosion but there could have been a threat from plutonium leakage.