China has stepped up repression in its ethnic Tibetan regions to prevent any protests during the Beijing Olympics, an activist group said.

Tibet, which Communist troops entered in 1950, witnessed violent rioting in March, which led to anti-government demonstrations across Tibetan areas of China, deeply embarrassing Beijing just months before the Games.

"To prevent potentially embarrassing protests inside Tibet, China has turned large parts of Tibet into a virtual prison for the duration of the Games," Matt Whitticase, spokesman for the Free Tibet Campaign, said in a statement.

The government's reaction to the Tibet unrest sparked demonstrations abroad that dogged the international leg of the Olympic torch relay and turned what was meant to be a symbol of Chinese unity into an obstacle course.

China poured security forces into its Tibetan areas, which extend across several western provinces, to quell the unrest, and the Free Tibet Campaign said the military build-up was accompanied by policies aimed at punishing activist monks and monasteries.

China's Foreign Ministry did not have any immediate comment.

But an editorial in the state-run China Daily said foreign countries had been unfairly critical of Beijing's treatment of its ethnic minorities.

"Many should feel ashamed of their groundless accusations once they know what the Chinese government has done for ethnic minorities," the English-language daily said.

The Dalai Lama, the spiritual leader of Tibetan Buddhism who has lived in exile in India since a failed 1959 uprising against Chinese rule, has said ongoing mistreatment of Tibetans violated Olympic values.

"Unfortunately the Olympic spirit is not being respected at all by Chinese officials in Tibet," he said in an interview in France on Saturday.

Chinese officials have said they oppose any link between Tibet and the Olympics. They see the issue as an internal affair and view the demonstrations as the work of a small group of people bent on Tibet independence.