The New York City Police Department increased its presence around the city Friday in response to an unconfirmed but "credible" terror threat coinciding with the 10th anniversary of the September 11th attacks.

The threat, which was first revealed Wednesday night, has not been corroborated but is based on information obtained while searching Osama Bin Laden's compound in Pakistan.

Mayor Michael Bloomberg and NYPD Commissioner Raymond Kelly announced plans for extra security checkpoints in and around New York City-area bridges and tunnels, as well as an increased effort in towing any illegally parked vehicles. People commuting through a tunnel or on a bridge are advised to be aware the drive may take a bit of extra time.

The Mayor says that there is no reason to change daily routines, but urges if someone sees something suspicious to call 3-11, and if someone sees something dangerous, to call 9-11.

"We take every single threat that is credible seriously," Bloomberg said at a press conference Friday.. "We may feel that it's more likely or less likely but you never want to say 'well we didn't think that was very likely' so we didn't do anything."

Thousands of police officers have been deployed to several hot spot areas in the city including Times Square, the World Trade Center site and Grand Central Station.

Authorities say the threat applies not only to New York City, but to Washington, D.C. as well.