BEIJING (Reuters) - Two young Tibetan monks set themselves on fire to protest against government religious controls in western China on Monday, two exiled Tibetan sources said, the third such protest this year that could spark fresh tension in the unstable region.

The 18-year-old monks, Kelsang and Kunchak, belong to the Kirti monastery -- a major site of protest against Chinese policies and the scene of a harsh crackdown by security forces in May -- one India-based exiled Tibetan activist, told Reuters.

The monks' self-immolations could lead to a renewed crackdown in Aba prefecture, a heavily ethnic Tibetan part of Sichuan province that many advocates of self-rule say should form part of a larger homeland under Tibetan control.

"When they set themselves on fire, they shouted: 'We need freedom of religion,'" said the activist, who asked not to be identified, adding that he obtained his information from at least five sources in China and overseas.

Both monks immolated themselves at 10 a.m. local time (0200GMT) on Monday, he said.

The two monks suffered slight burns and were in stable condition, state news agency Xinhua said, citing doctors. The report added that "the suicide attempt is under further investigation."

When asked about the self-immolations, Hu Jiang, an official from the Aba prefecture information office, told Reuters: "I don't know anything about it, I'm not quite clear."

Calls to the police bureau in Aba prefecture went unanswered.

A Tibetan monk, Kanyag Tsering, from the sister Kirti monastery in the Indian town of Dharamsala, where Tibet's government-in-exile is based, said he had received confirmation that the Chinese military removed the bodies of the two monks.

Tsering said he got his information from at least 10 different people inside the monastery and within Aba, including eyewitness accounts of the self-immolations.

Tsering said the two monks were heard shouting several slogans as they burned themselves, including: "Long live the Dalai Lama."

The self-immolations come just six months after another Tibetan Buddhist monk, Phuntsog, 21, from the same monastery, burned himself to death. [ID:nTOE72F08I]. Kelsang is related to Phuntsog.

China last month jailed three monks for their involvement in Phuntsog's self-immolation.

His death kicked off a harsh crackdown, with security forces detaining about 300 Tibetan monks for a month.

Monks from the Kirti monastery also participated in protests that gripped Tibet and Tibetan areas of China in March 2008, when Buddhist monks and other Tibetan loyal to their exiled spiritual leader the Dalai Lama confronted police and troops.

Beijing has repeatedly accused the Nobel Peace Prize-winning Dalai Lama of being a separatist who supports violence, charges he denies.

The Dalai Lama and China have argued lately about what should happen when he dies. Beijing says he has to reincarnate, but the Dalai Lama has questioned whether this tradition should continue.

"Like a has-been star, he fears the loss of popularity," the official Xinhua news agency wrote in a commentary. "In pursuit of fame and power, he has deviated from the commandments of Buddhism and used his religion as a subterfuge for his personal political motives."

"The Dalai Lama ... should seriously follow the teachings of Sakyamuni, the founder of Buddhism, and seek the dharma that will liberate him from the rotation of life and death," it added.

(Additional reporting by Sabrina Mao, Editing by Ben Blanchard and Sugita Katyal)