Beijing - A court in south-western China's Sichuan province has sentenced two Tibetan Buddhist nuns to nine and 10 years in prison after a court convicted them of crimes linked to protests last March, a Tibetan exile group reported on Friday.

The Ganzi (Kardze) County Intermediate People's Court sentenced the two nuns from the Pangri Na Convent for taking part in a mass protest in support of Tibetan autonomy and the exiled Dalai Lama, the Tibetan Centre for Human Rights and Democracy (TCHRD) said.

The two women, aged 35 and 36, were among 55 Buddhist nuns detained after a protest outside the Ganzi county government offices on March 18, the group said.

Police released most of the other nuns in September but up to a dozen were believed to be still in detention, it said.

Two 18-year-old Tibetan youths were also sentenced to three years in prison after they were arrested following the March 18 protests in Ganzi, TCHRD said.

But the exact date of sentencing and the charges against the four Tibetans was unclear, it said.

News of the sentences comes amid growing tension in Tibetan areas of China as paramilitary police try to prevent more protests around the anniversary of widespread protests last March.

Police in Litang town, which is part of Ganzi, this week arrested about 20 people after small protests, the Tibetan exile group said.

In the Tibet Autonomous Region, which borders Sichuan, top Communist Party, government and military officials this week held a video conference to discuss maintaining stability and "defeating separatism" during several sensitive anniversaries this year.

Last year's protests began in Lhasa, the regional capital, on March 10, the 49th anniversary of a failed Tibetan uprising against Chinese rule.

The government said 19 people were killed in the rioting but the Tibetan government-in-exile said about 140 people were killed, most of them Tibetans shot by Chinese paramilitary police.

Last week it said 76 people were sentenced to prison for their role in the Lhasa rioting.

Tibetan exiles have alleged that the government has intensified a crackdown in Tibetan areas in the run-up to the anniversary of the rioting and the 50th anniversary of the flight into exile of the Dalai Lama.

Officials have urged Tibetans not to join a campaign by exile groups for a boycott of the week-long Tibetan lunar new year celebrations, which begin February 23. (dpa)