Investigators Assess Threat of Bombing Tied to 9/11

WASHINGTON — Counterterrorism officials on Thursday were assessing a report about the threat of an attack in New York City or Washington using a car or truck bomb and timed to the 10th anniversary of the Sept. 11 attacks, according to several officials briefed on the matter.

In a statement, a spokesman for the Department of Homeland Security, Matt Chandler, called the threat “specific, credible, but unconfirmed.“ Another official said American intelligence agencies were urgently pursuing leads overseas in an effort to gauge the seriousness of the threat.

“It’s in the early stages, and a lot of vetting is being done in other places,” the official said.

At 9:45 Thursday night, Mayor Michael R. Bloomberg of New York and the city’s police commissioner, Raymond W. Kelly, said at a news conference that the police would set up vehicle checkpoints around the city, increase bag checks on the subway and keep a closer eye on bridges and tunnels.

The mayor noted that the threat information had not been corroborated and warned against an overreaction. He declined to speak about the nature of the threat report.

“The best thing we can do to fight terror is to not let it intimidate us,“ Mr. Bloomberg said, adding that he planned to take the subway in the morning as usual.

“I can tell you our ceremonies will go on over the weekend exactly as they were planned,” the mayor said, referring to the memorial events for the 10th anniversary.

The types of security precautions outlined by the New York Police Department suggested that the authorities believed the threat could involve a vehicle.

President Obama was first briefed on the threat on Thursday morning, and members of Congress were briefed during the day, officials said.

A White House official said that while the government had already stepped up its vigilance in advance of the anniversary, “the president directed the counterterrorism community to redouble its efforts in response to this credible but unconfirmed information.”

The report of the threat came after several quiet weeks in which officials said they were scanning intelligence with extra vigilance before the anniversary, but had found nothing credible.

Mr. Chandler noted that in a notebook seized after Osama bin Laden was killed, the Al Qaeda leader speculated about mounting an attack 10 years after Sept. 11 or on another symbolic date.

“As we always do before important dates like the anniversary of 9/11,” Mr. Chandler said. “We will undoubtedly get more reporting in the coming days. Sometimes this reporting is credible and warrants intense focus. Other times it lacks credibility and is highly unlikely to be reflective of real plots under way.”

But he said officials took all threat reports seriously. “We continue to ask the American people to remain vigilant as we head into the weekend,“ he said.

One law enforcement official said the initial intelligence report said that at least three suspects in a reported plot, one of them an American citizen, left Afghanistan and entered the United States by air last month. Intelligence agencies have not confirmed the report or identified those involved, the official said.

The official, who like others would speak of the investigation only on the condition of anonymity, said there was no connection to rental trucks reported missing in Kansas City, Mo. The trucks have been recovered and are not believed linked to the threat.

At the press conference, Commissioner Kelly described in detail steps the police department would take to increase security across the city.

Officers will work 12-hour shifts, instead of 8-hour shifts. Vehicle checkpoints will be installed. The police will conduct bomb sweeps in parking garages and elsewhere. More police cars will be equipped with cameras that scan passing license plates. Convoys of police cars will swoop down at predetermined spots in shows of force. Increased numbers of illegally parked cars will be towed.

“All of these precautions are on top of an already robust counterterrorism overlay in place for the 10th anniversary commemoration at the World Trade Center site.” Mr. Kelly said.

In a statement late Thursday, Gov. Andrew M. Cuomo sounded the same themes. “All New Yorkers should be cautious and aware as we prepare to commemorate the 9/11 anniversary,” he said. “However, there is no reason to panic or allow our spirit of freedom to be dampened as we get ready to celebrate the opening of the Ground Zero site this weekend.”