America currently faces "the most significant" threat since the Sept. 11, 2001 attacks, Homeland Security Secretary Tom Ridge said Monday.
Explaining Friday's elevation of the national terror-alert status, Ridge told CBS's The Early Show that "one of the reasons that we raised it is that because we believe the threat has substantially increased in the last couple of weeks."
The Bush administration raised the alert level from yellow (moderate) to orange (high), citing intelligence that it said suggested a growing threat from Usama bin Laden's Al Qaeda terrorist network.
On the five-step alert scale, red is the highest, but no such terrorist warning level has yet been issued.
Ridge and his deputies also advised various industries and local governments how to increase security in response to the threat.
On Friday, Homeland Security officials recommended that hotels inspect all cars, that malls and offices prohibit delivery trucks from entering underground parking garages, and that office tower managers control access at the door and monitor their heating and air conditioning ducts for breaches.
Terrorists could use chemical or biological weapons in ductwork to attack an entire building, officials said.
Monday, federal officials recommended that Americans should take basic disaster-preparation steps such as maintaining a three-day stockpile of food and water. They also recommended obtaining duct tape and plastic sheeting to seal a house in the event of a chemical or biological attack or disaster.
Homeland Security spokesman Gordon Johndroe said the recommendations for the household are not in response to the orange alert but instead just proper planning for disasters, including terrorist attacks.
Asked Monday what U.S. citizens are expected to do in response to such warnings, Ridge said, "When we raise the level of alert, when we raise the national consciousness about the level of attack, that in itself, is a deterrence. ... Just being more ready, being more prepared, is a deterrent in and of itself."
Ridge was questioned about the seriousness of the warning, which remains in effect.
"In discussing this matter with people that have been around the White House longer than I have, it is universally agreed that this is the most significant set of warnings that we've had since before Sept. 11," he replied.
Asked about critics' accusations that the alert might have been tied to President Bush's warning to Saddam Hussein that time is running out on Baghdad avoiding war, Ridge said, "Well, I regret that interpretation."
Appearing on NBC's Today program, Ridge said the warning was based on "the accumulation of credible corroborated sources, none of which are connected to the possibility of military involvement with Iraq."
Ridge, however, said it was not possible to be more specific about possible targets.
"We get general information and specific information, but none of the specific information talks about time, place or methods or means ... We don't get the specificity that we would all like to have in order to prepare," he said.
The Associated Press contributed to this report.