COMPLETE COVERAGE | FRONT LINES | AMERICA AT HOME | INTERACTIVES »

U.S. officials still on 'high alert' for additional attacks

By David Ensor
National Security Correspondent

WASHINGTON (CNN) -- Uneasy U.S. officials said they are still "on high alert" for additional attacks by Osama bin Laden's followers on U.S. soil.

"We get new threat information almost every hour" said one official. The information includes direct threats by phone, e-mail and fax, tips from foreign intelligence services, and intelligence gathered by the United States using sensitive electronic eavesdropping equipment.

CNN.COM SPECIAL REPORT  CNN NewsPass Video  Agencies reportedly got hijack tips in 1998  MORE STORIES Intelligence intercept led to Buffalo suspects Report cites warnings before 9/11  EXTRA INFORMATION Timeline: Who Knew What and When? Interactive: Terror Investigation Terror Warnings System Most wanted terrorists What looks suspicious? In-Depth: America Remembers In-Depth: Terror on Tape In-Depth: How prepared is your city?  RESOURCES On the Scene: Barbara Starr: Al Qaeda hunt expands? On the Scene: Peter Bergen: Getting al Qaeda to talk

Last week, the FBI issued a warning that there were indications another attack by terrorists could come "over the next several days." That time period has now passed, but there "is unfortunately no reason to stand down," said a U.S. official.

U.S. officials say that since September 11, a number of plots to attack U.S. targets overseas have been foiled, including plots against the U.S. Embassy in Paris, a U.S. facility in Turkey and the U.S. Embassy in Rome. In Brussels, Belgian police recently increased security around NATO facilities and officials, but U.S. officials say they are unaware of any specific and credible threat there.

A U.S. official said investigators do not have any indication yet whether the anthrax spores sent to a number of news organizations and others were sent " by wackos or by real terrorists."

Certainly, the official said, the anthrax scares could amount to a "low cost force multiplier" for terrorists, although a domestic source of the anthrax mailings is equally possible.

Officials said they have no evidence to date that bin Laden's al Qaeda group has ever used anthrax. Biological weapons experts said the biological agent is extremely difficult to turn into a weapon of mass destruction.

U.S. intelligence officials have said in the past they have evidence al Qaeda has tested chemical weapons on animals at a terrorist training camp in Afghanistan.