Swiss researchers who last November analysed a tape attributed to Osama bin Laden say they won't be scrutinising the latest recording broadcast by the Arabic television network, Al-Jazeera.
The Swiss analysts said the previous tape was almost certainly faked, despite US claims to the contrary.
The Dalle Molle Institute for Perceptual Artificial Intelligence (Idiap) in Martigny told swissinfo on Wednesday that it had no intention of analysing the latest tape.
United States officials say the recording, which calls on Muslims to fight the US and repel a war against Iraq, is "probably" the voice of Osama bin Laden, suggesting a link between Iraq and bin Laden's al-Qaeda network.
The US said a similar recording, broadcast by Al-Jazeera on November 12, was also genuine, despite analysis by Idiap researchers, who concluded that it was faked.
However, the company said the poor quality of that recording coupled with the limited number of voice examples meant that it was unlikely the recording could ever be properly authenticated.
The finding suggests that no one can say with certainty whether the November recording, or similar ones, are definitely the voice of bin Laden, as some US officials have claimed.
Idiap, based in Martigny in canton Valais, told swissinfo it had agreed to analyse the November tape, at the request of a French TV channel, for reasons "mainly motivated by pure scientific curiosity". It added that it therefore had no need to conduct further analyses on new recordings.
swissinfo, Jonas Hughes
US officials claim the recording broadcast on Tuesday is genuine.
A similar recording analysed by Swiss researchers last November was found to be fake.
That research suggests it is impossible to say for sure that the voice is bin Laden's.