Swiss researchers say they do not believe that the voice on a recently released audiotape is actually that of Osama Bin Laden. The tape was broadcast earlier this month by the Al-Jazeera, the Arabic language television channel. The French TV network, France 2, commissioned the experts to examine the recording.

Researchers at the Dalle Molle Institute in Lausanne, Switzerland compared the audiotape with 20 others that are believed to genuine. In a broadcast on the France 2 channel, they reported that they were 95 percent certain that the voice on the latest tape is not Osama bin Laden's.

One of the researchers said the recent tape was considerably different from the earlier recordings and the voice could be that of an impostor.

That conclusion contradicts American experts who said the tape, broadcast on November 12, was probably genuine, although it was of such poor quality that even the most sophisticated voice-print technology was inconclusive.

The speaker on the tape made reference to recent terrorist attacks in Bali, Indonesia, off the coast of Yemen and in Kuwait.

If genuine, it would be the first indication in more than a year that Mr. bin Laden is alive. American officials say the last known recording of him was made in December 2001, when radio messages were intercepted from the Tora Bora cave complex in Afghanistan. American and Afghan forces attacked the caves in hopes of killing or capturing the al-Qaida leader.

U.S. officials say if Mr. bin Laden is still alive, he may be hiding in Pakistan or Afghanistan. An offer of a $25 million reward for information on Mr. bin Laden's whereabouts has not produced any definite information.