Two "criminal suspects" killed a police officer before being shot dead in a Tibetan-inhabited area hit by a spate of protests against Beijing's rule, Chinese state media said on Monday.

The story in the official Ganzi Daily newspaper did not name the pair, but it appeared to confirm earlier reports that two ethnic Tibetans had been shot dead in southwest China's Sichuan province last week.

The Ganzi Daily said the three "suspects" had fired on police in Sichuan's Luhuo county after they were ordered to surrender, without giving further details.

According to Radio Free Asia (RFA) -- a US-funded group that broadcasts news in several languages including Tibetan -- police in Luhuo shot dead Yeshe Rigsal, a monk, and his brother on Thursday.

Officials in Ganzi prefecture refused to provide any more details when contacted by AFP.

Sichuan has been hit by a series of self-immolations by Tibetan Buddhists who allege they are suffering from religious and cultural repression at the hands of Chinese authorities in the region.

China has stepped up security across its vast Tibetan-inhabited region after at least two people were killed last month in clashes between police and locals in Luhuo.

The protests are the biggest to hit the region since March 2008, when riots broke out in the Tibetan capital Lhasa before spreading to other areas.

On Saturday, an 18-year-old Buddhist nun set herself on fire in Aba county, near Luhuo, later dying of her injuries, exile groups and Chinese state media have said.

This brings to at least 19 the number of people who have set themselves on fire in the past year in Tibetan-inhabited areas in protest over Chinese rule.

RFA reported that another three Tibetans self-immolated earlier this month in a remote village of Sichuan. However, local authorities quoted in the official Global Times newspaper have denied that account.

China has blamed much of the unrest on the Dalai Lama, Tibet's exiled spiritual leader and said the self-immolations were a form of terrorism.

Tibetans have long chafed under China's rule over the vast Tibetan plateau, accusing Beijing of curbing religious freedoms and eroding their culture and language, and these tensions have intensified over the past year.

But Beijing insists that Tibetans enjoy religious freedom and have benefited from improved living standards brought by China's economic expansion.