By Frank Gardner BBC Security Correspondent in Washington

The interrogation of three suspected Saudi members of al-Qaeda and their accomplices is under way in Morocco.

The Saudi government has sent its own investigators to the North African country and doubtless the CIA and Britain's SIS (Secret Intelligence Service) are taking a keen interest in the questioning.

Their trial, for an alleged plot to attack US and British warships, is yet to begin. But already reports are emerging of what al-Qaeda has been up to since it was driven out of its Afghan mountain strongholds late last year.

US intelligence experts say there is mounting evidence that al-Qaeda cells are now functioning largely independently of their leadership

According to The Washington Post, the Saudi detainees have revealed to their interrogators how they and other al-Qaeda members were ordered to escape from Afghanistan, move back to the countries they came from, re-establish themselves and then launch terrorist attacks when ready.

Information gleaned from the latest interviews shows how certain al-Qaeda members fanned out westwards from Pakistan, crossing the Gulf, then moving on to Europe and North Africa.

The aim appears to be to establish new bases for operations now that al-Qaeda's Afghan refuge has been made largely inoperable.

Here in Washington, US intelligence experts say there is mounting evidence that al-Qaeda cells are now functioning largely independently of their leadership.

Communication limited

They say that the cells received initial support and funding from senior members, and are now being left to get on with the job on their own.

"There is no question that the operation in Afghanistan has disrupted the leadership but it is worrisome that so many of the top leaders of al-Qaeda appear to be still at large," says Jim Steinberg, a senior figure in the National Security Council under Bill Clinton.

"At the same time, even if we were successful in tracking down Bin Laden and the other lieutenants we are still going to have a deep challenge because this is a very de-centralised organisation that will be able to carry on, even if those key figures are eliminated."

If anyone was in any doubt that al-Qaeda has the will - and sometimes the capability - to continue mounting operations, they need only look at what has happened already this year.

In Tunisia there was the bombing of a synagogue in April that killed 20 people.

Al-Qaeda is believed to have attacked a US warship in October 2000

In Pakistan there have been three strikes against Western targets - a church, a bus carrying French naval personnel and last week the US consulate in Karachi.

The perpetrators in Pakistan are thought to have been local extremists loosely linked to, but encouraged by, al-Qaeda.

Then there are the plans that failed, including the thwarted bid to attack US and British warships in the Mediterranean.

All of these, while still deadly, are relatively small operations compared to the big one everyone here fears that Osama Bin Laden still has up his sleeve.

If he is still alive, Bin Laden is unlikely to lose any sleep over the arrest of his suspected agents in Morocco.

The disruption of an alleged plan to blow a hole in a Western warship will be an irritation, but no great setback, for the man bent on bringing America to its knees.

After all, al-Qaeda is in this battle for the long term, and if the West is going to stay ahead of it, it will need eyes in the back of its head.