Counterterrorism officials said Thursday they were investigating credible intelligence information received within the last day and originating from the tribal areas of Pakistan.
A source told WNBC the information related to a plan to set off car or truck bombs in Washington or New York around the time of the 9/11 anniversary.
The intelligence indicated that three people would travel to the U.S. from Pakistan to carry out such an attack but there were no specifics in terms of timing or target.
AP reported that law enforcement officials will be told tonight to be on the lookout for three men "of Middle Eastern descent" and potentially traveling in a van. Officials say that while the information has some specificity, and the source has been credible in the past, it's uncorroborated.
The threat was so specific, and coming at a time of already heightened security just days before the 10th anniversary of the Sept. 11, 2001, attacks that it could not be ignored, one source said.
In response, the New York Police Department said it was increasing security which would be visible to the public immediately. While the overall threat alert has not been raised, one source said he would classify it as 5 or 6 out of 10 on the threat level.
Information gleaned from Osama bin Laden's compound in May indicated that al-Qaida had considered attacking the U.S. on the 10th anniversary and other important dates. Security has been enhanced around the country, including in New York and Washington, in the weeks leading to Sunday's anniversary.
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.
"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."
The threat came in a single piece of information and intelligence officials could not determine whether it was related to previous intelligence, the official said.
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.