U.S. military bases and diplomatic missions worldwide are also being placed on high alert for the week, officials say. The U.S. Embassy in Jakarta was closed Monday because of a specific threat against it.

The flurry of incoming threats picked up by intelligence sources is challenging the FBI to determine which might be credible. But while officials say they have no specific details of an impending attack, the government is taking no chances.

White House press secretary Ari Fleischer said Monday the threat of new attacks remains a worry to U.S. officials.

"Anniversaries can be - not necessarily always - can be occasions for heightened terrorist activity," Fleischer said. "Just given the fact that it's a one-year anniversary, we're going to be on our toes."

Last week, the FBI posted a bulletin on a Web site and sent a message over a private law enforcement bulletin system advising a state of alert on Sept. 11.

The police bulletin was sent Wednesday, according to a law enforcement official who spoke on condition of anonymity.

The Web site bulletin was posted by the FBI's National Infrastructure Protection Center, which assesses threats and passes warnings to local infrastructure companies and agencies. Banks, trucking companies, power companies, utility companies and transportation companies are in the network that the FBI communicates with through Internet bulletins.

Other events mentioned on the Web site as warranting heightened awareness include the Sept. 10-20 U.N. General Assembly session in New York and the Sept. 25-29 World Bank and International Monetary Fund meetings in Washington.

"A large volume of threats of undetermined reliability continues to be received and investigated by the FBI," the bulletin said. "Several of these threats make reference to the events of Sept. 11, 2001, and to New York City and Washington, D.C."

The warnings are based on information from all U.S. intelligence sources, from telephone calls to interviews with detainees at the U.S. Naval Base in Guantanamo Bay, Cuba, according to a senior law enforcement official.

Information from detainees, most of whom have been out of circulation for months, has proven false before. U.S. officials have said they act on it only when corroborated through multiple sources, but believe advising caution still is necessary.

In the run-up to the Sept. 11 anniversary, U.S. intelligence agencies have detected a marked increase in terrorist "chatter" - that is, monitored communications and other information used as a barometer of the likelihood of potential attacks.

Recent terror plots in Afghanistan and Germany, however, have not been linked to al-Qaida, said a U.S. counterterrorism official, speaking Monday on condition of anonymity.

In Germany, a Turkish man and his American fiancee, arrested last week on suspicion of plotting to bomb a U.S. military base in Heidelberg, are thought to have been inspired by Osama bin Laden, but U.S. officials doubt the pair is connected to the organization.

If that's the case, counterterror officials worry that the Turk, Osman Petmezci, and his fiancee, Astrid Eyzaguirre, may represent a new kind of threat wrought by the spectacular nature of the Sept. 11 attacks - people who have had no contact with al-Qaida but are moved to action by bin Laden.

U.S. military bases went on alert Monday out of an abundance of caution and not in response to any specific threat, government officials said.

At the State Department, spokesman Richard Boucher said a cable was sent to all diplomatic posts advising them to maintain a higher state of alert Wednesday. A worldwide July 1 caution urging Americans to take extra care remains in effect.

Along with the close of the embassy in Jakarta, the consulate in Surabaya was closed and officals said the U.S. Embassy in Manila was a source of concern.

The FBI bulletin did not cite specific intelligence of an attack at the United Nations but said such a New York City event in the general time frame of the Sept. 11 anniversary "represents a potentially attractive target for terrorists."

The bulletin said the World Bank demonstrations are planned by a "loose alliance of left-wing groups" and could result in property damage.

President Bush will mark Wednesday's anniversary of the attacks with a speech to the nation, followed by an address Thursday to the U.N. General Assembly.

(China Daily September 10, 2002)