U.S. counterterror officials said Thursday they have seen no specific or credible intelligence to indicate an upcoming Al Qaeda attack on the country, despite a new audio tape reporting preparations for such a mission.

While warning against downplaying the taped threat, purportedly from Usama bin Laden, officials at intelligence and law enforcement agencies said there also has been no recent increase in "chatter" that can indicate that such an attack is imminent.

Intelligence officials were trying to determine the authenticity of the tape, released by the television network Al-Jazeera Thursday morning. That process that could take between several hours or several days — and perhaps through the weekend.

Intelligence authorities were examining why bin Laden — if in fact the voice on the tape is verified as his — would be speaking out after more than a year of letting his top deputy, Ayman al-Zawahiri, serve as Al Qaeda's public face in statements and other communications.

"It isn't clear at this point what it means," said one counterterror official, speaking on condition of anonymity because of the sensitive nature of the tape. However, "one would think it might be an effort to demonstrate both to Al Qaeda rank-and-file and the public at large that that he's still around, given that he hasn't been heard from in such a long time."