Tibetans living in China's Ganzi and Aba prefectures -- rocked by violent clashes this week -- are renowned for their strong sense of identity and political activism, academics and activists said.

The rugged areas in the southwestern province of Sichuan are part of what used to be the Tibetan region of Kham, which for centuries was ruled separately from much of the neighbouring area now known as the Tibet Autonomous Region (TAR).

Tibetans living there are famous for their sense of independence from any regime -- be it Beijing now or Lhasa before that -- and for their willingness to fight despite their strong Buddhist beliefs, experts said.

"The area has historically been restive. These are areas that have always promoted and bravely shown their sense of Tibetan identity," Stephanie Brigden, director of the London-based advocacy group Free Tibet, told AFP.

Police shot dead protesters and fired tear gas to disperse crowds in three separate incidents this week, according to rights groups, in some of the worst unrest in Tibetan-inhabited areas since huge demonstrations against Chinese rule in 2008.

Advocacy groups say at least three people were killed in two clashes in Seda and Luhuo towns, but maintain the protests were peaceful until police fired into the crowds.

The Chinese government says two died -- one in each incident -- and acknowledged police shootings only in Seda, saying they had to use lethal force against violent protesters.

The unrest comes at a time of increasing tensions in Tibetan-inhabited areas, where at least 16 people have set themselves ablaze in less than a year -- mostly in Aba prefecture -- in protest against religious repression.

Aba and Ganzi cover more than 230,000 square kilometres (88,800 square miles), an area almost the size of the United Kingdom, and experts say the vast majority of the population is Tibetan.

An estimated 54 percent of all Tibetans now live outside the TAR -- which was formally established by the ruling Communist Party in 1965 -- with many in the bordering provinces of Qinghai, Sichuan and Yunnan, as well as Gansu.

In Sichuan, most of the 1.5 million Tibetans are concentrated in Ganzi and Aba. Elsewhere, the majority Han Chinese dominate, representing nearly 94 percent of the entire province's population, according to official figures.

Barry Sautman, an expert on the issue from Hong Kong University of Science and Technology, said Kham Tibetans were renowned for being "more willing to fight than other Tibetans".

He added the remoteness of the area had made it more difficult for Chinese security forces to control.

"These are frontier areas between areas of almost complete Tibetan concentration in the Tibet Autonomous Region and areas which are completely or almost completely Han (Chinese) on the edge of the Tibetan plateau," he said.

"This has had some effect in terms of maintaining a continuity of nationalistic thought."

Kate Saunders, spokeswoman for the US-based International Campaign for Tibet, said Tibetans in Ganzi had been more politically active than in most other Tibetan-inhabited areas of China.

She said they had expressed this in recent years "through demonstrations, prayer vigils, and solitary protests, in order to convey their loyalty to the Dalai Lama and their anguish" at repression.

The large number of monasteries scattered across Ganzi and Aba may also have contributed to the spate of unrest in recent years as monks -- resentful of propaganda campaigns aimed at making them renounce the Dalai Lama -- retaliate.

"If they have grievances, people in the area hear about those grievances and they -- the Kham people -- see it as their duty to protect the monks," Sautman said.

Beijing blames the Dalai Lama, who fled Tibet in 1959 after a failed uprising against Chinese rule, of fomenting unrest in a bid to split Tibet from the rest of China, which the Buddhist spiritual leader denies.

It insists that Tibetans enjoy freedom of religious belief and says their lives have been made better by huge ongoing investment into Tibetan-inhabited areas.

But many Tibetans reject this, saying they suffer religious repression and government surveillance, adding their culture is gradually being eroded by an influx of Han Chinese into the areas they live in.

These tensions turned into violence in March 2008 when deadly riots erupted in Lhasa, the capital of the TAR, and unrest spread to other Tibetan-inhabited areas including Aba and Ganzi.

Robert Barnett, a Tibet expert at Columbia University, said the latest violence appeared to be a continuation of the 2008 unrest.

"The grievances expressed in about 150 protests then were dismissed by the authorities as the result of outside agitation or of uncivilised behaviour, and so people's concerns about Chinese policies were not listened to," he said.