Swiss voice experts believe an audiotape attributed to al-Qaeda leader Osama bin Laden may be the work of an impostor.
The verdict follows analysis of the recording that was aired on al-Jazeera Arabic television earlier this month.
"It could be an impostor. We must remain prudent," researcher Mr Samy Bengio of the Lausanne-based Dalle Molle Institute for Perceptual Artificial Intelligence (IDIAP) said on Thursday. The IDIAP was asked by France 2 television to analyse the audio recording.
After compiling some 20 other bin Laden recordings, the institute was able to come up with a generic model of the al-Qaeda leader's voice and compared that with the audiotape broadcast by al-Jazeera on November 13th.
Mr Bengio said that although the recording was close, there were enough discrepancies to raise doubts about the authenticity of the bin Laden tape.
But US intelligence believed the recording was authentic and "almost certainly" the voice of bin Laden, officials said.
The finding appeared to confirm that the suspected mastermind of the September 11th attacks on the United States is alive and able to reach out to his followers, eluding a worldwide US-led manhunt.
AFP