With the 10th anniversary of the September 11 attacks just days away, U.S. counterterrorism officials have confirmed they have been chasing a credible al-Qaeda threat, CBS is reporting. The threat, which is still unconfirmed, involves a car bomb being used on bridges or tunnels in New York City or Washington, D.C. It was the first active plot to coincide with the commemoration of the 9/11 attacks that killed nearly 3,000 people.

As counterterrorism officials were investigating the threat, police in New York and Washington said they would increase their already stepped-up staffing levels. The threat comes from Pakistan, and what remains of al-Qaeda’s core leadership.

Officials have been wary after information was released from Osama bin Laden’s compound in Pakistan. The information indicated that al-Qaeda had considered attacking the U.S. on the 9/11 anniversary and other important American dates. Officials also grew concerned that terrorists would use the anniversary to retaliate against the U.S., in wake of bin Laden’s death.

The government reportedly decided to alert the public of the threat because there are enough specifics in the threat to make it more than aspirational. But officials have not yet raised the nation’s terror alert level, however.

Security has been enhanced across the country, in wake of the 10th anniversary. The FBI and Homeland Security Department also urged law enforcement nationwide to maintain increased security and be on the lookout for suspicious behavior.

Written by: Karen Benardello