Reporting from Washington — U.S. intelligence and law enforcement officials scrambled Friday to identify and find as many as three men who supposedly planned to travel from Afghanistan to detonate car bombs on bridges or in tunnels this weekend in New York and Washington.
Officials said they obtained specific but uncorroborated intelligence this week that two or three individuals with close ties to Al Qaeda leaders in Pakistan had entered the United States in a plot to disrupt events planned to commemorate the 10th anniversary of the Sept. 11 attacks.
Vice President Joe Biden told morning TV shows that the intelligence came from a "credible source."
"We cannot confirm it. We are doing everything in our power. All hands are on deck," Biden told NBC's "Today."
The men — possibly including a U.S. citizen — were said to have crossed by land from Pakistan to Afghanistan and then to have boarded a series of flights bound for the United States, possibly connecting through Dubai International Airport in the United Arab Emirates, according to a source who has read the intelligence and who spoke on condition of anonymity because of the sensitive nature of the information.
Al Qaeda's new leader and Osama bin Laden's former top aide, Ayman Zawahiri, is believed to have personally signed off on the plans, the source said.
If true, several senior U.S. counter-terrorism officials may have erred in recent weeks when they asserted that Zawahiri's influence was in doubt and that the direct threat from Al Qaeda's central leadership in Pakistan was largely eliminated. The latest intelligence suggests that the core group remains a force.
The FBI set up a round-the-clock unit in its Washington headquarters to coordinate the investigation.
The warning came from a single trusted source who has given correct information in the past, said a U.S. official who was not authorized to speak to the media. Intelligence officials do not have specific names or fragments of names of any suspects, the official added.
Traffic backed up at Manhattan's bridges and tunnels Friday as the New York Police Department set up vehicle checkpoints on nearby streets. Police searched parking garages and stepped up towing of illegally parked cars, and some officers wore portable monitors set to vibrate in the presence of unusual radiation. National Guard troops carrying assault rifles patrolled at Grand Central Terminal and Penn Station, the city's railroad hubs, and police officers increased checks of subway riders' bags.
In Washington, police and federal law enforcement increased security around government buildings and monuments.
Extra air marshals will fly on domestic flights this weekend, and foreign air carriers have been asked to step up screening of passengers bound for the U.S. In addition, the Transportation Security Administration will deploy more than 600 teams of bomb-sniffing dogs and bag inspectors on train platforms and subway systems around the country.
U.S. officials have warned of a possible attack timed to the Sept. 11 anniversary ever since Navy SEALs killed Bin Laden in Pakistan in early May. Thumb drives, computer files and other data collected during the raid on the Al Qaeda leader's compound indicated that he was determined to launch another high-casualty strike, but did not detail a specific plot.
The intelligence obtained this week was explicit enough to upgrade assessments of a general threat.
For the anniversary attacks, Bin Laden wanted to use well-trained Al Qaeda operatives, the source said, rather than amateurs, several of whom have botched terrorist attempts in recent years.
An Afghan immigrant, Najibullah Zazi, planned to detonate a homemade bomb in New York subways on the 8th anniversary of the Sept. 11 attacks two years ago, but he aborted the operation when he realized he was under FBI surveillance. He was arrested and pleaded guilty.
On May 1, 2010, Faisal Shahzad, a U.S. citizen born in Pakistan, attempted to set off a large car bomb in Times Square, but it failed to explode and authorities quickly disarmed it. He was arrested two days later and has been sentenced to life in prison.
Bin Laden "was clearly not happy" with the failed attacks, said the source, who is familiar with the documents recovered at Bin Laden's compound. The Al Qaeda founder wanted the next attack to be executed by seasoned operatives and closely managed by leaders of the organization.
Some of the increased security for this weekend was planned long ago in anticipation of an elevated threat during the anniversary, said a senior administration official who spoke on condition of anonymity because he was not authorized to speak to the media.
"We were concerned about this time period anyway because of the intelligence in the [Bin Laden] compound and also because of the iconic date," said the official. The new intelligence "may have been a new threat stream, but it wasn't a technique or a tactic we weren't prepared for," he added.
U.S. officials urged Americans to be extra vigilant in reporting suspicious activities to authorities.
Secretary of State Hillary Rodham Clinton, in an interview with CNBC from the floor of the New York Stock Exchange, said that by making the threat public, "you enlist literally millions of people to be your eyes and ears."
Homeland Security Secretary Janet Napolitano said in a statement, "Our security posture includes a number of measures both seen and unseen, and we will continue to respond appropriately to protect the American people from an evolving threat picture both in the coming days and beyond."