The United States warned late Thursday that it has picked up "specific, credible but unconfirmed" terrorist threats in connection with the tenth anniversary of the September 11, 2001 terrorist attacks.
New York Mayor Michael Bloomberg said the entire security apparatus in New York City has been heightened in response to intelligence that terrorist activities may have increased either in the city or in Washington.
Bloomberg said the New York Police Department, the FBI and the entire intelligence community have been on "heightened alert because we know terrorists view the anniversary as an opportunity to strike again."
"Threats at this moment have not been corroborated, I want to stress that," he said. "It's credible, but not corroborated. But we take those threats seriously."
Bloomberg urged New Yorkers to continue with their daily routine because of the deployment of additional police forces and undercover security throughout the city of 8 million inhabitants.
Police commissioner Raymond Kelly said security has been improved in bridges, tunnels, the transit system, including subways, hospitals and government offices.
Neither Bloomberg nor Kelly provided specific details of the additional police and security deployment. The city has more than 35,000 uniformed police officers and can make use of additional troops and undercover security forces as New York prepares for the 10th anniversary of 9/11.
U.S. Representative Peter King told CNN earlier that he had been briefed on the threat, along with other key members of Congress.
"The threat is specific, credible, but not confirmed," King said. "There is reason to believe it's true." US President Barack Obama has also been briefed on the threat, CNN reported.
King said intelligence officials were taking all the necessary steps to track down the threat.
CNN and other broadcasters reported that New York and Washington had been mentioned as targets.
According to broadcaster ABC, the CIA has been working for 24 hours on information that at least three individuals, including a US citizen, entered the United States in August with the intention of launching a bomb attack.
The suspects planned to use a bomb-laden vehicle to attack a target sometime around Sunday's 10th anniversary observations, according to unnamed intelligence officials cited by ABC. It was thought they had started their travels in Afghanistan or Pakistan.
Homeland Security Secretary Janet Napolitano told reporters earlier Thursday that there had been "lots of chatter" picked up by surveillance worldwide, and "we're taking it all seriously."
"Should there be something that rises to the level where I have to issue a threat advisory, we will issue a threat advisory," she said. According to the Homeland Security website, the alert level has not been raised.
"We know it's an iconic day to al-Qaeda, in part because of what was found at the (Osama bin Laden) compound. So we are preparing accordingly," she was quoted as saying.
After the group's leader Osama bin Laden was killed in May, US officials found evidence that he had been urging his followers to plan an attack on the US on the tenth anniversary of the US attacks.
Bin Laden was the mastermind behind the plot that saw terrorists hijack four passenger airplanes in 2001 and use them as missiles to destroy the World Trade Center twin towers in New York and damage the Pentagon.
The fourth plane was diverted by passengers from its likely second target in Washington, and crashed in Pennsylvania.
Nearly 3,000 people were killed in the attacks.
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