U.S. counterterrorism officials are investigating what they call a credible, but unconfirmed, terror threat planned to coincide with the 10th anniversary of the September 11 terrorist attacks on the United States.
Authorities in New York City and Washington, D.C. say they have increased police staffing in response to the threat, which is reported to focus on one of those two cities.
New York Mayor Michael Bloomberg has encouraged New Yorkers to continue their lives as usual.
Washington Mayor Vincent Gray said city authorities were taking precautions, working alongside federal agencies, to combat the threat. He declined to provide specific details, but urged residents to remain vigilant.
The mayors of both cities said the threat of an attack would not disrupt ceremonies on Sunday for the September 11 anniversary.
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.
The head of the Federal Bureau of Investigation's New York Division, Jan Fedarcyk, refused to name any specific group behind the threat. But she said information gathered in the U.S. raid on Osama bin Laden's compound in Pakistan last May showed that groups such as al-Qaida have an interest in specific dates.
Meanwhile, the White House said President Barack Obama has been continually updated on the threat. A White House official told reporters the president called on counterterrorism authorities to redouble their efforts to protect the U.S. from any attacks.
Separately Thursday, Homeland Security Secretary Janet Napolitano said intelligence officials have lately picked up more “chatter” on terrorist websites. She said the United States is taking all of the talk seriously.
Earlier this week, the U.S. government raised the alert level at its domestic military bases as a precaution ahead of the anniversary.
