By Mark Hosenball and Phil Stewart
WASHINGTON (Reuters) - While U.S. authorities are hunting two or three suspects behind a possible 9/11 anniversary attack threat, intelligence agencies are in the dark about the suspects' identities, officials said on Friday.
On Thursday, federal and New York City authorities disclosed that the U.S. had received specific and credible but uncorroborated intelligence indicating two or three individuals may have entered the U.S. as part of a possible plot to attack Washington or New York on the tenth anniversary of the September 11, 2001 attacks.
Officials said that the intelligence was received on Wednesday or Thursday, and was dramatic enough to change earlier assessments that there was no specific or credible intelligence of any plots to attack the U.S. on the 9/11 anniversary.
One official said that while lacking information about the identities of potential attackers, the intelligence was noteworthy because it was the first credible information alleging a specific attack plot related to the 9/11 anniversary.
The intelligence was "not run of the mill," a second official said. "Specific threats to the homeland don't come in every day."
The officials insisted on anonymity to discuss intelligence matters.
Because no names are associated with the latest threat intelligence, it will be extremely difficult for U.S. spy and law enforcement agencies to locate any suspects, one official said.
One reason U.S. agencies decided to make the threat information public was so that citizens would be extra-vigilant in reporting suspicious activity to authorities, the official said.
Two officials said the intelligence reporting alluded to the possibility of car bomb attacks in Washington or New York, though there was also uncertainty about the means.
The intelligence did not allude to threats against subways or commuter trains, although al Qaeda operatives had expressed interest in such attacks in the past, one official said.
Evidence of a desire to attack trains was recovered from a hide-out in Pakistan where U.S. commandos killed Osama bin Laden in May. And authorities in New York City said they are mounting a major show of force in subways and commuter railway hubs during Friday's afternoon rush hour.
There are conflicting reports about who might be behind the threat. One U.S. official told Reuters there is reason to believe that threat may be linked to Ayman Al-Zawahiri, the Egyptian doctor who assumed leadership of al Qaeda's central command after the bin Laden's death.
Secretary of State Hillary Clinton on Friday said that al Qaeda was behind the threat. But a third Federal official involved in the threat investigation said that while there were strong indications that people with Al Qaeda "ideology" were behind the threat, a direct tie to the remnants of Qaeda's central command was less clear.
(Editing by Warren Strobel)