U.S. authorities are scrambling to sort through information that the CIA developed in the past 24 hours indicating that at least three individuals entered the U.S. in August by air with the intent to launch a vehicle-borne attack against Washington, D.C. or New York around the anniversary of 9/11, according to intelligence officials.
Officials say the alleged terror plot was initiated by new al Qaeda chief Ayman al-Zawahiri, Osama bin Laden's successor, who had pledged to avenge bin Laden's death earlier this year in a U.S. raid.
Intelligence and law enforcement officials told ABC News that at least one of the individuals is a U.S. citizen and one official said that two of the individuals may have had U.S. documentation -- whether green cards or passports was unclear.
The threat was described as specific and credible by federal officials. "Al Qaeda has shown an interest in important dates and anniversaries. In this instance it is accurate that there is credible, specific but unconfirmed information," said Janice Fedarcyk, FBI Assistant Special Agent in Charge of the New York office, at a Thursday evening press conference.
At a the same press conference, New York City Mayor Mike Bloomberg said the NYPD was already on alert because the anniversary is seen by terrorists as an opportune time to strike, and would be deploying additional resources around the city. He also said that the threat was credible and had to be taken seriously, though "it has not been corroborated."
"We do live in a world where we must take these threats seriously and we certainly will," said Bloomberg.
As news of the information became public, authorities began weighing whether to raise the national threat level. The FBI and the Department of Homeland Security have sent a bulletin to 18,000 law enforcement agencies around the country warning them of the potential plot. The bulletin notes that al Qaeda might seek revenge for the death of bin Laden and other key figures on a symbolic date like the anniversary of 9/11.
Although authorities said they had not yet identified the suspects, they are looking at multiple names of individuals who entered the U.S. after mid-August. The operatives are believed to have embarked on their journey to the U.S. from the tribal areas of Pakistan, according to two senior officials. One official said the route may have taken them through Dubai.
The information on the plot was "very specific " said one official, adding " It seems like the information has been worked for a while." A second and third official confirmed the specifics of the possible plot added that a declassified bulletin is expected to be issued shortly.
Initially, one official added that at least two rental trucks -- one from Penske and one from Budget -- were being sought nationwide. Those trucks have since been recovered and appear to have had no connection to the plotters.