'They expressed doubts that this was probably some incident created by the Chinese Communist Party in an attempt to crack down on certain ethnic groups. I am very angry.'

Mr Baikeli said any attack on a civilian aircraft should be considered a terrorist attack.

'How can you apply double standards to this? It's unbelievable,' he said.

Exiled Uygur dissident Rebiya Kadeer was quoted by Agence France-Presse on Monday as accusing Beijing of fabricating the plots to taint the name of her community.

Chinese Foreign Ministry spokesman Qin Gang denied the accusation. 'These people, like Rebiya Kadeer, link the government's efforts to strike hard against terrorism and connect it to the majority of the Uygur people, which is extremely insidious.'

Terrorism, separatism and extremism have been named by the central government as major destabilising factors in predominantly Muslim Xinjiang.

Quoting an unnamed official, Global Times, a paper affiliated to the Communist Party's mouthpiece, People's Daily, reported yesterday that slack Xinjiang airport staff provided the opportunity for the attempted attack. A 19-year-old Uygur woman from Kuche, Xinjiang, was able to carry a mineral-water bottle and two beverage cans through security checks for business travellers manned by a relatively old guard at Urumqi airport.

Despite guidelines barring travellers from carrying beverages on board a plane, the paper said the security worker apparently dropped his guard to let the woman through after she took two mouthfuls from the bottle. The woman was later found locked in an aircraft toilet on China Southern flight CZ6901 with a number of cans filled with petrol.

The plane made an emergency landing in Lanzhou, Gansu, at about 12.40pm on Friday after leaving Urumqi at 10.35am.

None of the passengers or crew were hurt and the plane flew on to Beijing on Saturday morning after being held for several hours. Airline sources said four Uygurs, including the 19-year-old woman, were taken away by police for questioning.

Xinjiang party chief Wang Lequan said on Sunday, when officials for the first time revealed details of the foiled aircraft attack, that the Olympics were a target for the region's terrorists.

A group broken up in Urumqi in January was plotting to attack the Beijing Games in collaboration with the East Turkestan Islamic Movement, a Uygur group allegedly linked to al-Qaeda, Mr Wang said.

But officials have been quick to quash speculation that Olympic security will be threatened.

'We have the absolute ability and confidence to secure the Olympics security,' Mr Baikeli said. 'Our airport security is very well placed.'

However, according to the Global Times, the woman took several flights to assess airport and on-board facilities as well as security-check procedures so she could take advantage of the security lapse.

Mr Baikeli said the investigation was continuing but 'according to my personal analysis [this attack] must involve forces outside China'.