A Code Orange alert - the second most serious of all the government alerts - was declared on Tuesday and remains in effect. Code Orange is defined as a high alert - that is, the existence of a high risk of terrorist attacks.
On Wednesday, the government expanded the code orange alert to ban aircraft from flying within 3 miles of any major professional or collegiate sporting event as long as the nationwide terror alert remains at its second-highest level.
The Federal Aviation Administration notified pilots Wednesday morning of the new restrictions on aircrafts, including blimps and banner-towing planes. The restrictions also apply to any large outdoor gathering.
Officials said information from debriefings with a senior operative of Osama bin Laden's al Qaeda terror network, and from U.S. intelligence agencies, points to possible attacks on American facilities in southeast Asia or possible suicide attacks on U.S. interests by individuals in the Middle East.
U.S. military forces in the Middle East were upgraded to their highest alert status Wednesday in response to warnings of possible terror attacks on the anniversary of strikes against America, defense officials said.
Police departments throughout the 50 states are on alert and have urged anyone who sees anything suspicious to pick up the phone and report it.
A Northwest Airlines jet traveling from Memphis, Tennessee, to Las Vegas, was diverted Wednesday to Fort Smith airport in Arkansas, after three passengers locked themselves in a bathroom, officials said. No one was injured.
Police and firefighters surrounded the aircraft, which was parked at the end of a runway. Passengers were taken off the plane. Jim Harris, a spokesman for Gov. Mike Huckabee, said the men appeared to be of Middle Eastern descent.
In Washington, federal officials who spoke on condition of anonymity said the incident was not believed to be a terrorist incident.
In a separate incident, an American Airlines flight traveling from Houston to Nashville, Tenn. was escorted back to Bush Intercontinental Airport by F-16 fighters Wednesday afternoon after what FBI officials initially reported to be an attempted hijacking. No injuries were reported and the FBI said there had be no hijack attempt, but that a passenger had been removed from the plane.
Also Wednesday, a 41-story state office tower that houses the Ohio Supreme Court was evacuated after dogs detected a scent of explosives in a van at a loading dock, the State Highway Patrol said. Patrol spokesman Lt. John Born said a man was in custody. No explosives were found in the van, but the scent was detected three times by a dog, Born said. A man was taken into custody after he told a worker in the building that he was there "to install a bomb."
Meanwhile, Army Gen. Tommy Franks, head of the U.S. Central Command in Tampa, Florida, ordered the "Threat Condition Delta" protective alert for troops and their families throughout the Gulf, Middle East, Horn of Africa and parts of Central Asia, according to the officials, who asked not to be identified.
Forces in Bahrain, where the U.S. Fifth Fleet is based in the Gulf with some 4,000 troops, had been put on Delta Tuesday and other bases in the Central Command region were at that time placed on slightly lower "Threatcon Charlie."
That was upgraded Wednesday in a precautionary move.
The United States has told the Philippines of a plot by al Qaeda to bomb U.S. embassies with trucks and that such an attack could occur on or after Sept. 11, the presidential palace said on Thursday.
The Philippine ambassador to the United States, Albert del Rosario, mentioned the alleged plot in an "urgent and confidential message" to President Gloria Macapagal Arroyo, copies of which were released by the palace to reporters.
The New York Times quotes some government officials as saying the information that led to the Code Orange alert came from al Qaeda operative Omar al-Faruq, who was arrested in Indonesia several months ago.
Other government officials quoted by The Times say they received the information from an al Qaeda operative just this week, and the CIA was able to corroborate some of what was said by checking with other detainees and studying intercepted messages.
The government has promised extraordinary security and surveillance at events commemorating the attacks. President Bush, who will visit the three sites where some 3,000 people perished, is urging Americans to "go about their lives" as normal.
Even at Disneyland in Anaheim, Calif., CBS News Correspondent Steve Futterman reports there's heightened security, with random searches of bags and searches of every car parking at the Disneyland Hotel.
Futterman also found evidence of America's new concern about its borders at a crossing in San Diego, where people can enter the U.S. by land, by sea and by air.
"They have 150,000 crossings a day," said Adele Forsano, district director of the Immigration and Naturalization Service. "The major thing we've done is we've intensified our inspections."
The fear is of a terrorist or weapon of mass destruction entering the country.
Shortly after the Code Orange was announced, Vice President Dick Cheney was moved to a secret location as a security precaution. He will remain there throughout Sept. 11.
"We'll do everything we can to protect the American people," said President Bush said after Attorney General John Ashcroft announced the alert.
"U.S. intelligence has concluded that lower-level al Qaeda operatives may view the Sept. 11 anniversary as a suitable time to lash out in even small strikes to demonstrate their worldwide presence and resolve," said Ashcroft. "Widely dispersed, unsophisticated strikes are possible."
The U.S. attorney general says there is concern about "a full range of terrorist activities," with potential targets including transportation and energy networks, as well as symbols of American power, from embassies and military bases to corporate interests.
CBS News Correspondent Jim Stewart reports that a broad range of security measures are in place nationwide. National Guard troops are patrolling the Golden Gate Bridge in California. In Portland, Oregon, National Guard F-16s are on alert, and although there will be no additional flight restrictions, all estimated 6,000 air marshals will be on duty.
Under special rules for the Sept. 11 anniversary, airline passengers will also be required to stay seated for 30 minutes after takeoff and prior to landing at New York and Washington airports on Wednesday.
In response to the alert, nine U.S. embassies and consulates overseas have been closed, including some in Africa, where two U.S. embassies were bombed in 1998.
The headquarters of the U.S. Fifth Fleet in Bahrain, where some 4,000 sailors and other troops are based, was put on the highest alert. "We have credible information about threats against U.S. installations in the region," one official said.
Within the United States, officials promised tight security at the federal, state and local level, through a combination of combat air patrols and increased police and FBI presence at monuments and other key sites.
Around Washington, heat-seeking Stinger missiles will be deployed on military jeeps with firing and guidance units. "This is not a response to a specific threat. It is a prudent preparation to improve the air defense posture of the national capital region," one senior defense official said.
Across the country, access was restricted to public places and events. Colorado Gov. Bill Owens, announcing security measures at the state capitol, told residents, "You should probably bring your driver's license" to the building.
Due to being hidden at a secure location, Cheney was unable to appear at a scheduled speaking engagement, but he made his views clear nonetheless in videotaped remarks. Cheney expressed confidence in the ability of U.S. law enforcement and intelligence agencies to disrupt terrorist plots domestically and abroad.
But he added, "For every bit of progress we've achieved, all of us appreciate that we are still closer to the beginning of this war than to its end."
FEMA has activated emergency teams to monitor developments and coordinate a federal response if necessary.
The U.S. Customs Service has bolstered security at all of the nation's ports of entry by increasing vehicle, passenger, cargo, and mail searches.
The threat level of "orange" is one step below the highest alert, which is "red."
The level has stood at "yellow", the middle of the five-point scale, since the government created the system in March to offer people guidelines on how to prepare for any future attacks.