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Security has been enhanced around the country in the weeks leading up to the 10th anniversary, a date officials have long known could draw an attack. Law enforcement officials have been particularly wary after information gleaned from Osama bin Laden’s compound in Pakistan indicated that al Qaeda had considered attacking the U.S. on this anniversary and other important American dates. Officials have also been concerned that terrorists would see the anniversary as an opportunity to retaliate against the U.S. for killing bin Laden in a military raid in May.

Officials said that so far they have no reason to believe that there is a direct connection between this new threat and the information found in the compound laying out al Qaeda’s aspirational goals.

The FBI and Homeland Security Department issued a joint intelligence bulletin Thursday night to law enforcement around the country urging authorities to maintain increased security and be on the lookout for suspicious activity.

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, officials said.

“There is specific, credible but unconfirmed threat information,” the head of the FBI’s New York division, Janice Fedarcyk, said. “As we always do before important dates like the anniversary of 9/11, we will undoubtedly get more reporting in the coming days.”

New York Mayor Michael Bloomberg told reporters that police there were deploying additional resources around the city but that New Yorkers should go about their business as usual, and the city’s observance of the attacks will go on as planned.

In Washington, law enforcement officials said they were working 12-hour days indefinitely, and Police Chief Cathy Lanier said unattended cars parked in unusual locations risked being towed.

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

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

Intelligence officials had not seen any specific or credible threats regarding an attack around the anniversary before Wednesday.

Associated Press writers Matt Apuzzo, Lolita C. Baldor, Julie Pace and Eric Tucker in Washington and Tom Hays in New York contributed to this report.