U.S. officials say the threat of a car- or truck-bomb attack in New York or Washington as Americans mark the tenth anniversary of 9/11 is "specific, credible but unconfirmed." the New York Times reported on Friday.
The paper cited counter-terrorism officials who were briefed on the matter.
At a news conference on Thursday evening, New York Mayor Michael Bloomberg said the police would set up vehicle checkpoints throughout the city, step up bag checks in the subway and keep a close watch on bridges and tunnels.
The mayor cautioned that the threat report was uncorroborated.
"The best thing we can do to fight terror is to not let it intimidate us," Bloomberg said, adding that there would be no changes to plans for memorial ceremonies.
ABC News has reported that three individuals entered the U.S. in August on a mission to carry out a terror attack.
U.S. President Barak Obama and former president George W. Bush are scheduled to attend a ceremony at the site of the World Trade Center on September 11.