As the nation on high terror alert braced for busy holiday travel on Tuesday, airports beefed up security after reports surfaced that Al Qaeda (search) could be planning more attacks on the U.S. with commercial jets.

Officials at the Department of Homeland Security (search) said intelligence and electronic chatter indicated Usama bin Laden's terror network was hoping to launch strikes on large urban areas and even rural communities like Rappahannock, Va., which has several government facilities, and Valdez, Alaska, where tankers load oil from the Trans Alaska Pipeline (search).

U.S. officials said Tuesday they had received information from a credible source about an Al Qaeda threat against oil interests in Alaska, which they have not fully corroborated. Still, they were treating the information seriously and had implemented extra precautions.

Because of those communications, extensive security measures were in place in all 50 states and already-tight security was fortified at transportation and energy facilities nationwide.

Also on Tuesday, the U.S. embassy in Bahrain said it received information about a terrorist threat to Americans in the Gulf Arab state during the Christmas holiday.

Police in Turkey fear militants have infiltrated the country to organize attacks on U.S., Israeli and other Western interests or Istanbul's most popular shopping mall, according to an intelligence document.

And the State Department warned American citizens in Israel, the West Bank and Gaza to "remain vigilant."

Airport security was extremely heavy during the holiday week, and the Department of Homeland Security advised travelers to be patient and expect some inconveniences.

Bomb-sniffing canine units were added at Cincinnati/Northern Kentucky International Airport, maritime patrols were augmented near power plants that border Lake Erie and more officers than usual were activated along the U.S.-Canadian border.

Similar defenses have been increased around key bridges, tunnels, seaports and landmarks, as well as chemical facilities and other places that may be vulnerable to attack.

Other layers of protection likely have been in place since Sunday, when the national security level was bumped up to orange, which is "high" alert, from yellow or an "elevated" alert, security experts said.

"There's going to be a menu of visible and invisible measures that are implemented," said Brian Jenkins, research associate at the Mineta Transportation Institute at San Jose State University and a special adviser to the Rand Corp., a California-based think tank.

An increase in the number of air marshals, particularly on flights arriving from overseas, undercover surveillance around airports and more frequent air patrols near major cities are among the covert steps that probably were taken, Jenkins said.

There were some concerns about missiles being fired at planes taking off or landing, Jenkins added.

But there was no actual intelligence or intercepted chatter indicating Al Qaeda pilots were set to fly wide-body jets from other countries and crash them over the United States, Fox News learned.

Instead, U.S. officials and military personnel told Fox they've theorized that the greatest threat to airlines could involve plans using "complicit crews" — which could either be bogus crewmembers wearing stolen uniforms and bearing false identification or existing trained pilots and flight attendants aboard foreign carriers who agree to participate in a terror plot.

One U.S. official told Fox that discussions of such a scenario and methods of waging a successful counterattack have been ongoing.

Meanwhile, a new high-tech security measure will be added in January, when 115 major U.S. airports and seaports plan to begin scanning fingerprints and snapping photographs of foreigners entering the country by air and sea.

President Bush assured Americans that the government was doing everything it could to keep them safe during the holidays.

"American citizens need to go about their lives, but as they do so, they need to know that governments at all levels are working as hard as we possibly can to protect the American citizens," Bush said.

The fact that it's the holiday season, a time when many people are distracted, traveling and gathering at events like football games and New Year's celebrations, partly drove the decision to raise the alert.

However, authorities also said the move was based on specific, corroborated intelligence that Al Qaeda may soon try to pull off an attack in multiple places to cause mass casualties.

White House spokesman Scott McClellan said such an attack could eclipse those of Sept. 11, 2001, which killed nearly 3,000 people.

U.S. intelligence and law enforcement officials, speaking on condition of anonymity, said they did not have any specifics about a potential method, location or time of any attack. They noted that in light of the Sept. 11 attacks, aviation could be a prime possibility.

"We know, tragically, they turned four airplanes into missiles," Homeland Security Secretary Tom Ridge told reporters after a meeting of Bush's Homeland Security Council.

Defense Department officials said they were launching more military air patrols over major cities, but they would provide no details. Other government sources said, however, that New York, Washington and Los Angeles were likely choices.

The Transportation Security Administration (search), the federal agency charged with protecting air travelers, would not discuss its planning at a detailed level, other than to confirm that vehicle inspections and parking restrictions have increased at airports and that Coast Guard patrols have been added near airports bordering oceans and lakes.

"We're putting all hands on deck," TSA spokesman Darrin Kayser said, adding that parking restrictions may require travelers to park a little farther away than they might normally.

The Nuclear Energy Institute, which represents the owners of more than 100 reactors in 31 states, said the power industry is coordinating with law enforcement and intelligence agencies and has 7,000 of its own patrolmen at the ready.

"Really, it's a paramilitary security force," said Steve Kerekes, a spokesman for the group.

In addition, cargo planes and flights originating overseas were of special concern in the latest warning.

To defend against another airborne attack, baggage and passenger screeners are working overtime at airports, and their managers have come out from behind the scenes to work the front lines, the TSA said.

The Coast Guard, meanwhile, cautioned boaters to avoid off-limits areas near power plants and to keep their eyes peeled for suspicious activity.

Amtrak (search) said police officers are randomly riding and inspecting trains and that patrols have been beefed up inside stations and along platforms. Some baggage is also being checked, a spokesman said.

The Air Transport Association (search), which represents the country's major airlines, has urged travelers to arrive two hours before domestic or international flights and to check all bags in order to expedite the screening process.

Although commercial flight procedures have not changed as a result of the raised terror-threat level, the Federal Aviation Administration (search) has imposed stricter rules for private pilots flying in and out of airports near the nation's capital.

And a trucking industry trade group warned carriers of fuel or hazardous chemicals to be particularly alert.

Fox News' Kelly Wright, Ian McCaleb and The Associated Press contributed to this report.