"Two days after the U.S. government raised its terror alert to the second-highest level, Defense Secretary Donald Rumsfeld emphasized the gravity of the threat.

'You ask, 'Is it serious?' Yes, you bet your life. People don't do that unless it's a serious situation,' Rumsfeld told a Pentagon briefing.

The Defense Department conducted an exercise in which some Pentagon officials were moved to remote locations to practice maintaining leadership continuity over the U.S. military in the event of an attack, defense officials said. "