Despite signs, officials say no evidence of imminent attack

WASHINGTON -- There is not enough specific, credible evidence to believe another attack on America is imminent, despite warnings of increased terrorist activity, U.S. officials said Thursday.

The nation's terrorist threat level remains at code yellow, or "elevated," the middle of a five-point scale of risk developed by the Bush administration after the Sept 11, 2001, attacks.

Yet there is clearly worry that the danger is growing because of increased "chatter" picked up through intelligence channels, the continuing U.S. showdown with Iraq and the recently revealed taped warnings believed to be from al-Qaida leader Osama bin Laden.

"While we are not raising the threat level, we are taking additional precautions to meet the threat," White House spokesman Scott McClellan said.

These include unspecified "additional steps to ramp up our protection and prevention measures" within federal agencies, McClellan said. The FBI and other agencies also are communicating possible threats and assessments of risk to state and local law enforcement agencies and specific industries that could be targeted.

Heightened risk

In recent weeks, the FBI has issued warnings about possible attacks on U.S. railroads and on the energy industry, as well as a more general warning about heightened risk during the Muslim holy month of Ramadan, which started Wednesday and ends Dec. 5.

On Wednesday, the FBI told authorities in Houston, Chicago, San Francisco and Washington to be aware of threats against hospitals. Even though that threat was assigned low credibility by senior law enforcement officials, the FBI is preferring to err on the side of caution in terms of giving out information, officials said.