The US military has launched an investigation into how a B-52 bomber flew the length of the US mistakenly loaded with nuclear weapons. BBC world affairs correspondent Nick Childs considers the political and military fallout from the incident.
The US Air Force is investigating how one of its bombers mistakenly flew six nuclear warheads across the United States last week without anyone knowing about it.
US officials insist there was never any risk to public safety. And experts agree there was no danger of an accidental nuclear explosion.
The missiles were mounted on the wings of a B-52 bomber
But it is still difficult to overestimate the embarrassment to the Pentagon, and especially the US Air Force, caused by this incident.
Nuclear weapons are the "crown jewels" in the US arsenal, and are meant to be protected by many safety procedures.
The US military is not supposed to lose track of them, even for a few hours.
As well as the investigation, there is likely to be a major review of the way the US Air Force handles its weapons.
The political embarrassment lies in the fact that the Bush administration has made much of its worries about nuclear proliferation.
Washington has made no secret of its concerns over the years about the safety and security of the ex-Soviet nuclear arsenal, and whether those weapons might fall into the hands of terrorists.
The Pentagon's awkwardness over the incident was clear.
Its chief spokesman said publicly that he could neither confirm nor deny what happened, because the department does not discuss nuclear weapons procedures.
But he did say that what he called "an error in the transfer of munitions" took place.
And it was sufficiently serious that US President George Bush and US Defence Secretary Robert Gates were informed, and Mr Gates has had daily updates since.