Fearful of new terror attacks but armed with little specific information, the government warned potential targets to be on high alert in the run-up to the Sept. 11 anniversary.

While officials say they have no details outlining an impending attack, they're taking no chances.

The FBI told police, utilities, banks and the transportation industry to be wary. U.S. military bases and diplomatic missions worldwide also are on high security alert for the week.

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.''

The State Department issued a worldwide caution Monday night urging Americans to remain especially vigilant this week.

In the past few days, U.S. intelligence agencies have detected what officials now describe as a marked increase in terrorist ``chatter,'' information from monitored communications and other sources that are used as a barometer of the likelihood of potential attacks.

The FBI's National Infrastructure Protection Center, which assesses threats to key utilities and infrastructure, issued a general alert last week.

``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.''

Other events mentioned on the Web site as warranting increased 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.

The warnings are based on information from all U.S. intelligence sources, from telephone calls to interviews with detainees at the U.S. Navy 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 previously. U.S. officials have said they act on it only when corroborated through multiple sources.

Recent terror plots in Afghanistan and Germany 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. and German 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 care remains in effect.

The U.S. Embassy in Manila in the Philippines was believed to be of particular concern for potential terrorist strikes. And in nearby Indonesia, U.S. officials barred the public until further notice from the embassy in Jakarta and the consulate in Surabaya after receiving ``credible and specific threat information'' Monday that the embassy is at risk of terrorist attack.

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.''

``It is expected that some individuals plan to engage in criminal activity aimed at disrupting the meeting and drawing attention to their cause,'' the bulletin said. ``Historically, tiny contingents of individuals associated with the protests belonged to violent groups. Those groups have a history of causing 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.