WASHINGTON – Counterterrorism officials said Thursday they are investigating a credible but unconfirmed terror threat involving New York or Washington.

The threat was so specific, and coming at a time of already heightened security just days before the 10th anniversary of the Sept. 11 attacks, that it could not be ignored, a counterterrorism official said.

Officials would not say what specifically is being targeted in New York or Washington or the timing of a potential attack. A government official said the terror alert has not been raised because of the threat.

A law enforcement official in New York, speaking on condition of anonymity to discuss sensitive security information, described the threat as credible but declined to give details.

Information gleaned from Osama bin Laden’s compound in May indicated that al-Qaida had considered attacking the United States on the 10th anniversary and other important dates. Security has been enhanced around the country, including in New York and Washington, in the weeks leading up to Sunday’s anniversary.

President Obama was briefed on the threat information Thursday morning and directed the counterterrorism community to redouble its efforts in response to the credible but unconfirmed information, a White House official said.