California (CNN) -- Gov. Gray Davis said Thursday state officials had received a "credible threat" against four major bridges that could be the target of terrorists during rush hour between November 2 and 7.
He called for an immediate strengthening of security at the bridges in San Francisco, Los Angeles and San Diego.
"The best preparation is to let the terrorists know: We know what you're up to. We're ready. It's not going to succeed," he told reporters at a news conference.
He said the threat involved the Golden Gate Bridge and Bay Bridge in the San Francisco area, the Vincent Thomas Bridge at the Port of Los Angeles, and the Coronado Bridge in San Diego.
"We believe there is a credible threat that there will be an effort made between November 2 and November 7 to destroy one of those bridges" during rush hour, Davis said.
The governor said he came forward because "it's our obligation to inform the public."
"We don't want any damage. We don't want any bloodshed," he said. "Our goal is to be prepared."
FBI Special Agent Matt McLaughlin told CNN the information came to the FBI through another intelligence agency and that the FBI "is currently working vigorously to determine the credibility of the information."
Mindy Tucker, spokeswoman for Attorney General John Ashcroft, called the threat "uncorroborated" and said it is "not as credible as the information which prompted the threat warning Monday."
Ashcroft and FBI Director Robert Mueller said Monday intelligence information deemed "credible" indicated a possible threat to the United States or U.S. interests abroad in the coming week.
Surprised by Davis' statement, the Justice Department took the rare step of releasing a statement from the FBI Counterterrorism Division sent via the National Threat Warning System:
"The FBI is in possession of uncorroborated information indicating the possibility of additional terrorist attacks against the United States, specifically the West Coast," the statement said.
"Reportedly, unspecified groups are targeting suspension bridges on the West Coast. Six incidents are to take place during rush hour beginning Friday, November 2 and continuing through November 7, 2001."
"No further information about the alleged attack is known at this time," the statement continued. "The FBI is attempting to verify the validity of this report. Recipients will be updated as events warrant."
Justice officials noted the use of the word "uncorroborated" in the warning.
Officials at the governors' offices in Washington state and Oregon said they had no information of a "credible threat" in their states.
An official at the White House said the "uncorroborated" information was touched on during Thursday morning's intelligence briefing and that it was to be passed on to local law enforcement agencies.
"This is just part of the continued efforts to contact specific local law enforcement authorities when we believe it is necessary," the official said.
During his news conference, Davis said security was heightened at the bridges two weeks ago after two suspicious suitcases were found at the Golden Gate Bridge. He said the suitcases later turned out "not to be particularly worrisome."
Since then, he said, "we had taken elaborate security measures" with highway patrol, the Coast Guard and other officials to beef up security.
Davis said he also authorized an unspecified number of National Guard troops to protect the four bridges.
"We are providing extra vessel patrol and additional port police officers on land to patrol around bridge infrastructure," Capt. Martin Renteria of the Los Angeles Port Police told CNN. "We're also working with California Highway Patrol."
Renteria said the beefed-up security is a direct response to the governor's warning. He said the port police were notified Thursday morning about the threat by a federal agency, which he did not identify.
Capt. Ken Franke with the San Diego Harbor Police would not elaborate on specifics about security at the Coronado Bridge.
"Rest assured there's a very intensive security program in and around the bridge," he said.
California Highway Patrol spokesman Tom Marshall said National Guard troops were aiding the patrol with protecting the bridges.