By Frank Gardner BBC security correspondent

A broadcast purporting to have come from al-Qaeda's spokesman, Sulaiman Abu Ghaith, will have sent shivers down many a Western spine.

The message, aired on Sunday by Qatar-based al-Jazeera television, gloated that Osama bin Laden was alive and well.

It also claimed that 98% of al-Qaeda's leadership had survived the fighting in Afghanistan.

The first question to ask is: is the message genuine?

The answer is almost certainly yes.

Bombing claim

The message is consistent with reports coming out of Saudi Arabia that Bin Laden plans to grace the world's TV screens again soon.

The alleged al-Qaeda audio broadcast, carried earlier on an internet web site, also claims responsibility for the bombing of a synagogue in Tunisia which killed 19 people in April, including 14 German tourists.

Al-Qaeda leadership at large

Leader Osama bin Laden Senior adviser Ayman al-Zawahiri Spokesman Sulaiman Abu Ghaith Taleban spiritual leader Mullah Mohammed Omar

German investigators had already concluded that al-Qaeda was probably responsible for the blast.

So is it credible to claim that 98% of al-Qaeda's leaders escaped unhurt and are running its affairs unaffected?

Not surprisingly, the US military says no.

On Monday, the US spokesman at Bagram air base, Lieutenant-Colonel Roger King, described the claim as ''wishful thinking''.

Al-Qaeda leadership accounted for

Military chief Muhammad Atef: dead Chief strategist Abu Zubaydah: captured Chief recruiter Abu Zubair al-Haili: captured

He was quoted as saying: ''We felt that we have had a significant impact on [al-Qaeda's] ability to perform command and control. We do not feel that they can successfully do that with large bodies of forces at this time.''

There is no question that al-Qaeda's command structure has been severely disrupted in recent months.

Its military chief, Muhammad Atef, was killed in an air raid in November. So was a member of Bin Laden's inner cabinet.

Mullah Omar: no sign of one of the key US targets

His chief strategist, Abu Zubaydah, was captured earlier this year in Pakistan and is still being interrogated by the US.

And now, Abu Zubair al-Haili, one of al-Qaeda's key recruiters, has been arrested by Moroccan authorities.

But the uncomfortable truth for Washington is that its forces have still failed to capture either Bin Laden or his Taleban host, Mullah Mohammed Omar.

Massive attack

Both men are thought to be hiding in an obscure part of Afghanistan or Pakistan.

In the broadcast alleged to have come from al-Qaeda, the Islamist organisation gloated that Bin Laden would soon make a reappearance in a television interview.

In Saudi Arabia, al-Qaeda supporters say they believe that Bin Laden will make that broadcast in person only after a second, massive attack takes place in the United States.

And despite the optimism expressed by the US military on the ground in Afghanistan, it is exactly that doomsday scenario that is keeping awake the counter-terrorism strategists in Washington.