Self-immolation has been a form of political protest since the 1960s, but its use by Tibetans in China is a relatively new phenomenon, which rights activists say illustrates the desperation of Buddhist monks and nuns.

The Dalai Lama, the Tibetan spiritual leader, has expressed opposition to the practice, which experts say goes against Buddhist ideas on the sanctity of life.

Rights groups say eight Tibetan monks and former monks and one nun have now set themselves alight in southwest China's Tibetan areas since March and at least five have died. Here is a list of the most recent cases.

February 27, 2009:

Tabe, a Tibetan monk in his 20s from the Kirti Tibetan Buddhist monastery in China's Sichuan province pours petrol over himself and sets himself alight before being surrounded by police and taken away to an unknown location.

March 16, 2011:

Phuntsog, a Kirti monk whose age rights groups put at around 21, dies after setting light to himself on the third anniversary of riots in the Tibetan capital Lhasa, sparking protests that lead to a police clampdown in the area.

August 15, 2011:

Tsewang Norbu, a 29-year-old monk from the Nyitso Monastery in Sichuan, dies after setting himself alight.

September 26, 2011:

Two young Kirti monks, Lobsang Kalsang and Lobsang Konchok, thought to be aged between 18 and 19, die after setting themselves alight. Lobsang Kalsang is said to be the brother of Phuntsog.

October 3, 2011:

Kirti monk Kalsang Wangchuk, aged 17 or 18, sets himself alight, reportedly carrying a photograph of the Dalai Lama. Police put out the flames and take him away alive.

October 7, 2011:

Two former monks, Choepel, 19 and Khayang, 18, reportedly set themselves alight in Aba, the town where the Kirti monastery is located, and are taken to hospital. Both are believed to have died from their injuries.

October 15, 2011:

Norbu Dathul, 19, reportedly sets himself on fire in Aba Town. Local sources say Chinese police extinguished the flames and took the former monk away to an unknown location.

October 17, 2011:

Tibetan nun Tenzin Wangmo, 20, calls for religious freedom as she self-immolates outside the Mame Nunnery in Aba Town.

The residents of the Kirti monastery -- one of the most important in Tibetan Buddhism -- have been living under these siege-like conditions since a young monk set light to himself in protest at religious repression in March and died.

Since then, rights groups say five monks have burned themselves to death at the monastery in the small town of Aba, where a Buddhist nun this week became the first woman to self-immolate in a dramatic escalation of the protests.

Hours after the death of the nun Tenzin Wangmo on Monday, two AFP journalists gained rare access to the town in Sichuan province, high on the Tibetan plateau and famous for its centuries-old Buddhist temples.

Rights groups say nine monks and nuns have now set themselves alight in Sichuan and surrounding areas, with Aba town and the Kirti monastery becoming a flashpoint for the mounting anger at the erosion of Tibetan culture.

Police, many carrying riot shields and armed with clubs and iron, lined the streets of the town, which has a population of around 20,000 mainly ethnic Tibetans who say their culture is being eroded by China's government.

Large groups of soldiers in camouflage carried automatic rifles, metal rods with spiked tips and fire extinguishers, while police buses, trucks and armoured personnel carriers blocked the streets.

Shops and restaurants remained open and people went about their daily business on the streets of Aba, but police were checking all vehicles moving in and out of the town, slowing traffic through the main street to a crawl.

AFP's reporters were unable to gain access to the Kirti monastery, but saw large groups of police stationed outside the sprawling complex, as red-robed monks walked around inside.

Campaign groups Free Tibet and the International Campaign for Tibet (ICT) say there used to be more than 2,000 monks living in the monastery, but the number has now dwindled to fewer than 1,000.

They say that in recent months hundreds of monks have left the monastery, some of them taken away by authorities to undergo compulsory "patriotic re-education" programmes, and that the recent spate of self-immolations is a sign of the desperation they feel.

Many Tibetans in China are angry about what they see as growing domination by the country's majority Han ethnic group.

The latest government crackdown in the area was sparked by the death in March of Phuntsog, a young Kirti monk who set himself on fire on the third anniversary of anti-Chinese riots that shook Lhasa in March 2008, the bloodiest in Tibet in 20 years.

His death sparked mass protests in Aba and the surrounding area, known as Aba county.

Last month, China jailed three monks for between 10 and 13 years for helping Phuntsog to burn himself to death, sparking an international outcry.

Few, if any, foreign journalists have gained access to the town since then and AFP's reporters were briefly detained by police, who confiscated one camera and deleted photographs of police and the military presence.

"You can take pictures of all the scenery you want, but you cannot take pictures here," one policeman said. "You are free to leave. You must not stop until you have left (Aba) county."