CNN reports that the White House and legislators have been briefed on a "specific, credible but unconfirmed threat" to NYC and Washington D.C. The threat is said to involve car bombs of some sort, but details are sketchy right now. However, the legislators were told that officials are "strongly concerned" and "are not taking anything for granted."

Matthew Chandler, spokesman for the Department of Homeland Security, confirmed the reports, and released the statement below:

It's accurate that there is specific, credible but unconfirmed threat information. As we always do before important dates like the anniversary of 9/11, 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.

Regardless, we take all threat reporting seriously, and we have taken, and will continue to take, all steps necessary to mitigate any threats that arise. We continue to ask the American people to remain vigilant as we head into the weekend.

Chandler further explained what he meant about the "important dates": "As we know from the intelligence gathered from the [bin Laden] raid, Al Qaeda has shown an interest in important dates and anniversaries, such as 9/11." The threat was estimated to be on a level of 5 or 6 on a scale of 1 to 10, according to the report.

Update 8:30 p.m.: Mayor Bloomberg, the NYPD, and the FBI will hold a joint press conference tonight at 9:30 p.m. regarding the possible 9/11-anniversary threat.

Update 9:00 p.m.: A counterterrorism official told the Wall Street Journal that al Qaeda leaders in Pakistan are believed to be behind the alleged car bombings plot. "For the first time, the U.S. has received specific and credible but unconfirmed threat information linked to the 9/11 anniversary...[Al Qaeda has] been knocked back on their heels, but they will try to attack the U.S. any way they can," the official added.

Update 10:10 p.m.: Mayor Bloomberg, the FBI's NY Director Jan Fedarcyk, and NYPD Commissioner Ray Kelly are holding a press conference, emphasizing this is a "specific, credible but unconfirmed" threat. Bloomberg said that NYC has already been on heightened alert, but the police will increase its presence: "We live in a world where we need take these threats seriously," but "There's no reason for the rest of us to change the way we live our lives."

Bloomberg added that we should be vigilant: "If see something, say something... The best thing... is not to be intimidated by" a terror threat. Which means Bloomberg is taking the subway tomorrow morning. He added, "The NYPD will be deploying addition people around city. some of which you may notice, some of which you will not notice."

Fedarcyk said that Al Qaeda likes to plan around anniversaries: "We'll get more reporting in the coming days. We take all threat reporting seriously." However, she wouldn't get specific about who was making the threats, saying that until they can corroborate it, it's not clear if it's "operational or aspirational."

Kelly said that NYPD tours would be extended by four hours through Monday, which will effectively increase police presence by a third. There will also be increased police patrolling infrastructure, bridges and tunnels—especially in Grand Central, Penn Station and Times Square. In addition, there will be more bomb-sniffing dogs, more car checkpoints, increased towing, and more subway bag checks.

Bloomberg pointed out, "The public is the best eyes and ears that law enforcement has" and told the public to call 311 if they see something suspicious and to call 911 if it's something dangerous. He noted hopefully, "We've lived for 10 years with potential for terrorist attacks, NYPD has stopped at least 13 potential attacks."