By the BBC's Linden Kemkaran

Is he alive or is he dead? The White House seem to think it is the former, with a military official saying on Wednesday that they view the latest taped message from Osama Bin Laden as the first independent proof in nearly a year, that he is alive.

But without absolute proof, the frustrating game of cat-and-mouse continues.

Voice experts examining the vocal patterns and use of language on the tape, conclude that it is authentic. Medical scrutiny paints a picture of an injured Bin Laden, speaking in a hoarse voice with frequent pauses for breath.

The taped message praises the Bali bombing

The content of the tape certainly bears all the hallmarks of previous Bin Laden performances, although without him in vision we cannot be certain.

Previously the tall, bearded, enigmatic figure has appeared in a series of video releases, applauding the martyrs who gave their lives for the cause, smiling modestly as his companions excitedly re-live the moment the twin towers fell.

But what appears to make this tape genuine is that the speaker follows Bin Laden's tradition of praising recent atrocities in Bali, Kuwait, Yemen and Moscow, but not directly claiming responsibility himself.

This technique of referring to recent world events has been used by Bin Laden before. It is the audio equivalent (although not as foolproof) of having your picture taken with a copy of today's newspaper.

Ideological leader

So what if the tape does prove to be genuine? He may be alive but does it mean that he is still al-Qaeda's director of operations?

Experts think that since Al-Qaeda's base was driven out of Afghanistan and effectively scattered around the world, Bin Laden is now more of an ideological figure-head rather than the direct controller for attacks.

Communication between al-Qaeda and its followers is now much more difficult. They cannot use satellite phones, e-mail or facsimile messages as the intelligence services will detect them.

It is possible they have reverted to old fashioned means of communication - perhaps as basic as putting a messenger on a plane with a verbal instruction to be given to an al-Qaeda cell half-way across the world.

The worry is now that this tape is a pre-cursor to another terrorist attack

But as we know from experience, the cell structure is usually tightly organised with minimum communication between chief organiser and bomber.

For example, the person who is arrested for supplying false documents or a stolen car, often does not know who he was passing them onto or for what purpose.

The foot soldiers are kept well away from each other to avoid the risk of the top man being identified if one of them is caught.

Mood of fear

The worry is now that this tape is a pre-cursor to another attack.

The release of an al-Qaeda statement on 6 October by Bin Laden's deputy, Ayman al-Zawahiri, was followed six days later by the Bali blasts.

Perhaps another sign that a fresh attack is imminent came from a US law enforcement official on Tuesday.

He said that the level of "chatter" among suspected terrorists has reached the level seen before September 11.

But whatever happens next, confirmation that Bin Laden is alive will almost certainly prove to an anxious public that the war on terror is far from over.