New York City Michael Bloomberg says the city is heightening security in response to information about a “credible” but so far unconfirmed threat of a specific attack planned to coincide with the 10th anniversary of the September 11, 2001 terrorist attacks.

Speaking at the same press conference Thursday night, police commissioner Ray Kelly said the extra security measures would include vehicle checkpoints around New York City, bag checks at the subway, and teams equipped with bomb-sniffing dogs and radiation-monitoring equipment posted around the city. He said police were especially focusing their attention on tunnels, bridges and other major infrastructure, as well as landmarks, government buildings, and houses of worship.

Kelly said there would also be more police on duty in the next several days, which they will accomplish by extending shifts by four hours,

Mayor Bloomberg said New Yorkers should continue to be vigilant and report anything suspicious or apparently dangerous to the proper authorities. But the mayor said despite the threat, New Yorkers should continue their lives as usual. He said he expected to take the subway to work Friday morning feeling “just as safe” as he had Thursday morning.

U.S. officials said Thursday they had discovered information the “credible threat” suggesting it may focus on Washington, DC or New York City. Officials say they suspect three individuals, one a U.S. citizen, entered the U.S. in August intending to attack with a bomb-laden vehicle.

The White House said President Barack Obama was updated on the threat information throughout the day. A White House official told reporters the government had already “significantly enhanced” security and readiness efforts in advance of the September 11 anniversary, but the President Thursday called on counterterrorism authorities to “redouble” their efforts to protect the U.S. from any attacks.

Officials say the threat is unconfirmed and that they are continuing to investigate. They say they are considering whether to brief local police about what to look for and whether to make the information public. The government is also considering whether to raise the country's terrorist alert level.

Earlier Thursday, Homeland Security Secretary Janet Napolitano said intelligence officials have lately picked up more “chatter” on terrorist websites. She said the U.S. is taking all of the talk seriously.

Earlier this week, the United States raised the alert level at its domestic military bases as a precaution.