Federal, state and local authorities across the United States are stepping up security measures after Tuesday's decision to raise the national terror alert status to "high."
From the skyscrapers of Manhattan to the sunny beaches of southern California, America is once again on high alert in anticipation of a possible terrorist attack.
In New York, Governor George Pataki has decided to use National Guard troops to keep watch on key bridges and train and subway stations.
"We are calling up additional National Guard and we are assigning additional [New York] State Police to everything from the trains, the commuter trains in the metropolitan area to infrastructure around the state to the Canadian border," said Mr. Pataki.
In Los Angeles, police are now working 12-hour shifts as they step up patrols around more than 600 potential targets in the nation's second-largest city.
Los Angeles Police Chief William Bratton told NBC television that his officers are ready for whatever might be coming.
"Professionally, I think, we are about as prepared as we can be," he said. "We have good intelligence sources. We have great coordination efforts out here. And God forbid, if something should happen out here, I think we are as prepared as we could be to respond to that."
Chief Bratton is among a host of local officials who complain that the federal government has not provided millions of dollars in aid to states and cities to cover the increased costs of homeland security.
Despite the heightened awareness, President Bush says the United States continues to make progress in the war on terrorism. The president told the graduating class at the U.S. Coast Guard Academy in Connecticut Wednesday that nearly one-half of al-Qaida's senior operatives have been either killed or captured.
"We have seen the ruthless intentions of our enemies and they are seeing our intentions," said the president. "We will press on until this danger to our country and to the world is ended."
Homeland security officials elevated the terror alert level to orange, or "high", after considering various intelligence information including what is commonly referred to as "intelligence chatter."
Chatter includes intercepted phone and e-mail communications among people with suspected ties to terrorist groups. The increase in chatter followed the recent terrorist suicide bomb attacks in Saudi Arabia and Morocco, leading officials to believe al-Qaida or other groups might be planning similar attacks on the U.S. homeland.
U.S. intelligence officials say the new threats were generally vague in nature but there were some references to the northeastern cities of New York, Boston and Washington.
Massachusetts Governor Mitt Romney says security is being beefed up at a wide variety of venues including Boston's Logan Airport and Fenway Park, home of major league baseball's Boston Red Sox.
"My understanding is that there may have been in the [intelligence] chatter indications that mention the Northeast, but nothing at the level of credibility or that could be confirmed that would suggest a different status alert for the Northeast relative to any other part of the country," Mr. Romney said.
Terrorism experts say a spike or jump in suspicious chatter has been a past indicator that terrorist groups may be planning an attack.
"It is not always clear what they are saying because they sometimes speak in codes," said John Philipps of the Hudson Institute in Washington, when he spoke with VOA News Now. "But when the frequency goes up, it is a sign often that they are planning something."
Homeland security officials say the terrorist threats could come from any one of several groups. But they acknowledge the principal threat comes from al-Qaida, which U.S. and Saudi officials believe was behind the recent attacks in Riyadh.
"They have been regrouping," said David Heyman, a terrorism expert with the Center for Strategic and International Studies in Washington on VOA-TV's Newsline program. "They have been changing their tactics. They have been learning and watching, which is what they have been doing for years, but they have been learning and watching how the U.S. has adjusted its homeland security capabilities. And I think we are going to see more attacks in the future."
Homeland Security chief Tom Ridge is urging local authorities to pay particular attention to large public gatherings planned around the country during the upcoming Memorial Day holiday weekend.