Terrorists are likely becoming cleverer

“New York, Washington tighten security amid probe of bomb threat

A handful of individuals, one of whom could be a U.S. citizen, may have entered the United States in recent days as part of the suspected plot, which officials said originated from the tribal areas of Pakistan along the Afghan border.

A U.S. official briefed on the threat said it is based on intelligence that the CIA collected from a source in Afghanistan who has previously provided reliable information.

Officials said Friday that little had changed since the warnings first became public Thursday night. “I don’t get the sense that there’s been some new nugget of information that has heightened the intensity of [the investigation] or that they’ve discounted the information,” said another U.S. official briefed on the warnings. “The fact that this was recently received, from a reliable source, near September 11, with specific cities and a specific mode of delivery of a weapon — that crossed the threshold, got people to say we have to run every lead to the ground.”

Numerous officials familiar with the information cautioned Thursday night that while the threat is specific and worrisome, it is based on raw intelligence that is unconfirmed. Law enforcement agencies across the Eastern Seaboard were scrambling to determine how serious the danger is and to find any possible terrorist plotters.

Even as investigators continued their work, government officials said Americans should not allow fear of an attack to alter their daily lives.

“We are determined not to let the specter of terrorism darken the national character that has always been America’s asset,” Secretary of State Hillary Rodham Clinton said Friday in a speech marking the upcoming 9/11 anniversary. She added that investigators are “taking all necessary steps” to protect the nation.

On Capitol Hill, Terrance W. Gainer, the Senate’s sergeant at arms and a member of the board of the U.S. Capitol Police, said in a e-mail to senators, aides and others that “there is no reason to change the way we each conduct our daily business.”

“Frankly, the threat is not unexpected considering what has been learned in the past few months,” he wrote. “The whiff of a threat to attack U.S. interests on the 10th anniversary of the 9/11 attacks has been floated.” He added that Thursday’s government warnings were “well-intentioned, perhaps helpful, but not very well-coordinated.””