WASHINGTON -- Security is being increased at airports, borders and ports as the nation stands at "Code Orange," the second-highest alert level for terrorist threats.
The upgrade Sunday from "Code Yellow," or "elevated" status, followed warnings from the government that al-Qaida militants may be plotting attacks on America during the holidays. The new designation indicates a high risk.
"The information we have indicates that extremists abroad are anticipating near-term attacks that they believe will either rival or exceed" the Sept. 11, 2001 attacks, Homeland Security Secretary Tom Ridge said in announcing the change.
Some of the intelligence information gathered, Ridge said, indicates that Osama bin Laden's terrorist network is seeking again to use planes as weapons. They are "constantly evaluating procedures ... to find gaps in our security posture that could be exploited," he said.
The threat information comes from multiple, credible sources, but officials are unaware of a specific target or means of attack, said a senior law enforcement official who spoke on condition of anonymity.
Some of the intercepted communications and other intelligence mentions New York, Washington and unspecified cities on the West Coast, this official said. Authorities also are concerned about dams, bridges, nuclear plants, chemical facilities and other public works.
Thousands of state and local law enforcement agencies have received an FBI advisory urging special notice of sites that could be a conceivable target and potential security upgrades, the official said.
In addition, Ridge has contacted his counterparts in Canada and Mexico about increasing border security.
At a hastily arranged news conference Sunday, Ridge said credible intelligence sources "suggest the possibility of attacks against the homeland around the holiday season and beyond."
He said the government decided to raise the alert level after U.S. intelligence agencies "received a substantial increase in the volume of threat-related intelligence reports."
Hours after Ridge's announcement, the State Department issued a worldwide caution warning U.S. citizens overseas that they may be terrorist targets. Echoing Ridge, the caution said officials "expect al-Qaida will strive for new attacks designed to be more devastating" than the Sept. 11 attacks.
Ridge said officials did not see a connection between the recent capture of ousted Iraqi leader Saddam Hussein and the heightened security alert.
He also tried to reassure Americans traveling by plane for the holidays. "Make no mistake about it, aviation is far more secure than it's ever been in the history of the country," Ridge said. At the same time, he said security at airports can be ramped up a bit more.
As a result of the change in threat level, all federal departments and agencies were putting action plans in place and stepping up security at airports, border crossings and ports, Ridge said.
"Extensive and considerable protections have been or soon will be in place all across the country," Ridge said. "Your government will stand at the ready 24 hours a day, seven days a week, to stop terrorism during the holiday season and beyond."
And he urged Americans not to disrupt holiday plans. "If you've got travel plans, travel," he said.
In recent days, U.S. officials told travelers to be vigilant about the threat of attacks. The warning was prompted in part by a raised level of ominous intercepted communications that has not quieted for months.
On Friday, the Arabic television network Al-Jazeera aired a new threatening statement from Ayman al-Zawahri, bin Laden's chief deputy. The CIA said Saturday it believes the tape is authentic.
Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said Sunday that officials were trying to determine whether the increased material detected was an aberration or something more serious.
The alert level has previously been raised from yellow to orange four times -- setting off a flurry of increased security measures by cities, states and businesses.
The lowest two levels, green and blue, and the highest -- red, indicating an imminent threat -- have not been used since the system was put in place in March 2002.
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Associated Press writers Curt Anderson and John J. Lumpkin in Washington contributed to this report.