Washington, D.C. ? A B-52 bomber was mistakenly armed with six nuclear warheads and flown for more than three hours across several states last week, prompting an Air Force investigation and the firing of one commander, Pentagon officials said Wednesday.

The incident was so serious that President Bush and Defense Secretary Robert Gates were quickly informed and Gates has asked for daily briefings on the Air Force probe, said Defense Department press secretary Geoff Morrell. He said, “At no time was the public in danger.”

Rep. Ike Skelton, chairman of the House Armed Services Committee, called the mishandling of the weapons “deeply disturbing” and said the committee would press the military for details. Rep. Edward J. Markey, a senior member of the Homeland Security Committee, said it was “absolutely inexcusable.”

“Nothing like this has ever been reported before and we have been assured for decades that it was impossible,” said Markey, D-Mass., co-chairman of the House task force on nonproliferation.

The plane was carrying advanced cruise missiles from Minot Air Force Base, N.D., to Barksdale Air Force Base, La., on Aug. 30.