WASHINGTON , September 11 (IslamOnline & News Agencies) - With fighter jets patrolling the skies and the terror alert system to be increased to “orange”, Americans prepare to commemorate the worst terror attacks in their history with a day of solemn events and prayers set to culminate in an address by U.S. President George W. Bush.

Still stunned at how hijackers evaded America ’s security systems to use planes as instruments of terror, the nation will on Wednesday, September 11, mourn the 3,034 people who died in the September 11 attacks, amid warnings of new terror strikes.

Special religious and memorial services will mark the day along with broadcasts replaying the horrific footage of the landmark World Trade Center - a symbol of New York and of U.S. economic might - ablaze, then collapsing in a cataclysmic tableau of destruction.

Bush will lead the country in Wednesday’s ceremonies to commemorate the attacks, in which three hijacked airliners crashed into the twin World Trade Center towers in New York and the Pentagon just outside Washington .

A fourth hijacked jet crashed in Pennsylvania after passengers tackled the hijackers, preventing it from reaching what some experts believe was meant to be another key site, perhaps the White House.

After a day of religious services, Bush and his wife Laura will head for Ground Zero, where the president will lay a wreath in memory of the more than 2,800 people killed at the World Trade Center .

He will later give a nationwide address from New York .

For his part, Vice President Dick Cheney spent Monday night at a secret location, the White House said Tuesday.

“I will confirm that the vice president last night spent the night at a secure, undisclosed location, as was the case last year,” White House spokesman Ari Fleischer told a press briefing.

He said the action was “based on an on-going review of information as received, as well a precautions, a combination of the two, which makes these determinations necessary.”

Cheney disappeared from view for several days after the September 11 attacks as a major security shield was thrown around the Bush administration.

Security is tight with fighter jets that have been patrolling skies over major U.S. cities since Friday and nuclear plants, airports, bridges, monuments, shopping centers and public buildings all under closer-than-usual watch.

The U.S. State Department warned of the threat of new terror strikes against its interests worldwide on the anniversary, urging Americans around the world to be “especially vigilant.”

“There is a continuing threat of terrorist actions, which may target civilians and include suicide operations,” the department said in a new worldwide caution to Americans amid fears of attacks on U.S. embassies in Jakarta , Kuala Lumpur and Manila .

Three embassies in Asia , including Jakarta , have been closed because of increasing threats. U.S. Ambassador to Indonesia Ralph Boyce said there was a “specific terrorist threat against our embassy.”

The elevated risk (yellow) alert level in effect since shortly after the attacks on Washington , New York and Pennsylvania will be raised to high risk (orange) because of a specific and credible report of possible terrorist attack by Attorney General John D. Ashcroft, according to the Department of Homeland Security.

The change will be announced at a press conference late Tuesday, marking the first time the level has been heightened since the color-coded alert system was implemented in March, reports the Washington Post.

No specific mention was mode of any threat, but sources said the information received by government intelligence officials was deemed credible.

One government official, however, said, "We have evidence of operational activity in the United States and in other places around the world…The sources of some of this have been identified, some have not.”

The newspaper reports that under the alert system, orange signifies that federal departments and agencies should consider coordinating with armed forces and law enforcement; take additional precautions at public events; prepare to move to an alternate site; and restrict access to essential personnel only.

The warning system has five levels, starting with green - the lowest alert level - and followed by blue, yellow, orange and red. The latter is the highest alert level, indicating a severe threat, reports CNN.

The National Protection Infrastructure Center, under the Federal Bureau of Investigation (FBI), issued a bulletin recommending extra caution.

On commercial airliners, passengers will be required to remain seated for 30 minutes before takeoff and landing, the so-called “30-minute rule” already in force since last October at Reagan National Airport near downtown Washington.

Health officials also have said they are preparing for a chemical, biological or nuclear attack.

The FBI last week urged extra vigilance at power plants, electrical and water utilities and transportation operators - particularly those in New York and Washington - as the anniversary approaches.

In explaining the reasoning behind increased security, Fleischer said, “As the anniversary approaches, our concerns increase and that’s based on information that we’ve obtained. That’s also based on historical facts about what anniversaries mean. ... Anniversaries can be occasions - not always are but can be occasions - for terrorists to attack again. We’re cognizant of that, we’re vigilant about that.”

In capital cities across the world, events are being planned to commemorate the day that redrew the global geo-political map.

Stock exchanges across the world are due to hold a minute’s silence for the victims of the attacks, of all different nationalities, many of whom worked in the global financial markets.