The threat involving possible bombings was shared with New York and Washington police.
The threat information was about three people who may have been dispatched to the U.S. to meet with associates to carry out the attacks, said a federal law enforcement official who was not authorized to speak publicly and asked not be identified.
President Obama was briefed about the matter Thursday morning and received updates during the day.
Department of Homeland Security spokesman Matt Chandler said documents recovered from the raid in May on Osama bin Laden's compound in Pakistan revealed al-Qaeda's interest to strike the U.S. on meaningful dates.
"In this instance, it's accurate that there is specific, credible but unconfirmed threat information," Chandler said. "As we always do before important dates like the anniversary of 9/11, we will undoubtedly get more reporting in the coming days."
New York Mayor Michael Bloomberg said the threat, while credible, was "not corroborated." He urged New Yorkers to go about their business as usual.
I know the Police will do everything in their power to keep everyone safe.