Credible terrorist threat possibly planned for Sept. 11

U.S. officials said Thursday they were investigating a detailed al-Qaida car bomb plot aimed at bridges or tunnels in New York City or Washington to coincide with the 10th anniversary of the Sept. 11 attacks, the first tip of an "active plot" targeting that date.

The Homeland Security Department said the threat is credible and specific, but unconfirmed. The nation's terror alert level has not changed, but it was under consideration Thursday night.

Security has been enhanced around the country in the weeks leading up to the 10th anniversary. Law enforcement officials have been wary, particularly after information gleaned from Osama bin Laden's compound in May indicated that al-Qaida had considered attacking the U.S. on the anniversary and other important dates.

Law enforcement officials were investigating three people who recently entered the U.S. The threat came in late Wednesday night and is the first tip the U.S. intelligence community has received about an "active plot" targeting the anniversary, officials said.

The threat came in a single piece of information and was so specific — and came at such a time of already heightened alert — that it could not be ignored. The officials described the threat to The Associated Press on condition of anonymity to discuss sensitive security matters.

New York Mayor Michael Bloomberg and Police Commissioner Raymond Kelly planned an evening news conference to discuss the threat.

President Barack Obama was briefed on the threat information Thursday morning and directed the counterterrorism community to redouble its efforts in response to the credible but unconfirmed information, a White House official said.

White House officials said there were no plans to change Obama's travel schedule on Sunday in light of the threat. The president is scheduled to mark the 9/11 anniversary with stops at New York's ground zero, the Pentagon and Shanksville, Pa. He will also deliver remarks Sunday night at a memorial concert at the Kennedy Center in Washington.

"It's accurate that there is specific, credible but unconfirmed threat information," Homeland Security Department spokesman Matt Chandler said in a statement. "As we always do before important dates like the anniversary of 9/11, we will undoubtedly get more reporting in the coming days."

Law enforcement officials are checking out all of the details included in the threat, Rep. Peter King, R-N.Y.

"No need to panic," King said. "They have not been able to confirm it yet."

Thursday morning, Homeland Security Secretary Janet Napolitano told reporters that there was "a lot of chatter" around the anniversary of the attacks but that there was no information about a specific threat.