The reference sparked a flurry of behind-the-scenes intrigue as international intelligence agencies tried to probe the veracity of the news. Previously, Thailand had not featured in any significant fashion in the known facts of the 9/11 plot.

The formal US investigation into the attacks said that al-Qaeda planners ordered the hijackers to obtain new 'clean' passports, not fake ones.

'It was an incredible statement,' said one western diplomatic security official, referring to the Thai reports. 'Nothing like this involving 9/11 has surfaced before.' Others described it as laughable.

Unusually, Thai Prime Minister Abhisit Vejjajiva mounted a swift retreat. While police were still investigating the trio's activities, there was nothing firm to link them to foreign terrorists or local insurgents, he said.

The case appears to be a reminder that elements within the Thai security forces are determined, wherever possible, to blacken the reputation of the Rohingya, a persecuted tribe from Myanmar whose members have been fleeing to Thailand in growing numbers.

Claiming they represented a security threat, the army conducted a secret policy of detaining Rohingya boatpeople on an isolated island before towing them to sea in unpowered boats. At least 1,190 were abandoned and hundreds died.

Mr Abhisit, facing international condemnation over the policy, has recently insisted it will not be repeated when a new sailing season starts in the winter.

While they may be exploited by criminals and snakeheads, all evidence suggests Rohingya are simply seeking a better life, rather than aiming to cause mayhem in the south or further afield.

Reports provided to the South China Morning Post from Stirling Assynt, a well-sourced global business risk assessment firm, suggest that al-Qaeda gave up on the Rohingya as potential jihadists more than a decade ago.

A Stirling assessment says that senior Bosnian mujahideen veterans once considered the Rohingya's home in Myanmar's Rhakine state as a potential new front for jihad after the end of the Bosnian war in 1995. A delegation travelled to the Bangladesh/Myanmar border to meet Rohingya but formed a damning opinion of the chances of a Rohingya insurgency.

According to the Stirling assessment, the mujahideen found the Rohingya to be 'hopelessly undersupplied, disorganised, ill-disciplined, unmotivated and lacking of even basic jihadi principles'.

Any hope that jihad could be exported to Myanmar was dropped and has never been revisited by al-Qaeda strategists.

Al-Qaeda's links to the long-running separatist campaign in Thailand's Muslim deep south are not particularly strong either, with locals determined to keep it a locally run, if bloody, affair.

Al-Qaeda sent a pair of mid-ranked operatives to the region in 2006 for four months of training, including bomb-making, but they left with the conclusion that their local allies were not suitable for global jihad either, Stirling says.

Given the shadowy nature of those behind the almost-daily violence in southern Thailand, and their precise intentions, it appears Thailand's security forces have their work cut out at home, before they start spreading their nets abroad.