WASHINGTON - The United States put its subways, buses and commuter trains on high alert after the rush-hour London bombings, moving to code orange for mass transit amid concern about a possible "copycat attack" by terrorists.
From New York to San Francisco, cities tightened security for local rail and bus lines that carry tens of millions of Americans daily. Stepped-up safeguards included bomb-sniffing dogs, increased video surveillance and more police at train and bus stations.
Homeland Security Secretary Michael Chertoff said Thursday that authorities had no evidence of a specific, credible threat against the United States.
However, he said, "we feel that, at least in the short term, we should raise the level here because, obviously, we're concerned about the possibility of a copycat attack."
The London attacks were well-coordinated, leading to speculation about al-Qaida involvement, and U.S. officials were trying to determine responsibility.
U.S. counterterror officials said they received intelligence last month dating back to 2004 that al-Qaida was interested in attacking rail systems in Europe and the United States, including derailing trains or crashing trucks into them. The officials, who spoke on condition of anonymity because the intelligence is classified, said the report lacked specifics on the date and location of any potential attacks.
Security around the Capitol and at foreign embassies in Washington was increased, particularly around the British Embassy. Law enforcement authorities around the country were urged to step up security at United Kingdom diplomatic offices, and the State Department ordered U.S. embassies around the world to review their security arrangements.
"We will not yield to these people, will not yield to the terrorists," President Bush said in Gleneagles, Scotland, where he was attending the Group of Eight summit. "We will find them. We will bring them to justice."
Signing a condolence book at the British Embassy in Washington, Secretary of State Condoleezza Rice wrote of Thursday's bombing victims, "They will not have died in vain."
At the State Department, a British flag was run up a flagpole outside the diplomatic entrance and then lowered to half-staff by two uniformed guards.