China said on Monday it had shown massive restraint in the face of violent protests by Tibetans, which it said were orchestrated by followers of the Dalai Lama to wreck the Beijing Olympics in August.

But even as the governor of Tibet told reporters in Beijing that no lethal weapons had been used against protesters in the capital, Lhasa, troops poured into neighbouring provinces to quell copycat protests and riots that erupted over the weekend.

A resident in Sichuan's Aba prefecture said fresh protests flared in two Tibetan schools on Monday, with hundreds of students from each facing off against police and troops.

The resident, who declined to be identified, said 18 people, including Buddhist monks and students, were killed when troops opened fire with guns on Sunday. Earlier a policeman was burnt to death.

His account could not be immediately verified.

Exiled representatives of Tibet in Dharamsala, India, on Sunday put the death toll from last week's protests in Lhasa at 80.

But Qiangba Puncog, the government chief of the Himalayan region, said that only 13 "innocent civilians" had been killed and dozens of security personnel injured in Lhasa when several days of monk-led protests broadened into riots in which houses and shops were burned and looted on Friday.

"I can say with all responsibility we did not use lethal weapons, including opening fire," he said in Beijing, adding that only tear gas and water cannon had been used to deal with the region's worst protests in nearly two decades.

The governor said the unrest was planned and organised by "external and domestic forces" of the "Dalai clique", referring to Tibetan Buddhists' exiled spiritual leader, the Dalai Lama.

"This time a tiny handful of separatists and lawless elements engaged in extreme acts with the goal of generating even more publicity to wreck stability during this crucial period of the Olympic Games - over 18 years of hard-won stability."

Peng Xiaobo, who sells clothes in Lhasa, told state television seven family members were forced to jump from an upper floor when a mob set his ground-floor shop on fire.

His uncle and cousin were burned to death, while his wife suffered serious injuries, CCTV said.

"My cousin only turned 18 in December. She didn't dare jump when the stairs below were burning," Peng said in tears.

The Dalai Lama fled Tibet after a failed uprising against Chinese rule in 1959 and set up a government-in-exile in Dharamsala. Beijing reviles him as a separatist though he says he only wants more autonomy for the region, which Communist troops entered in 1950. The last major rioting in Tibet was in 1989.

MIDNIGHT DEADLINE

Tibet is one of several potential flashpoints for the ruling Communist party at a time of heightened attention on China ahead of the Olympic Games.

The government is concerned about the effect of inflation and wealth gaps on social stability after years of breakneck economic growth, and this month it said it had foiled two plots hatched by the members of the Muslim Uighur population in the northwestern region of Xinjiang, including an attempt to disrupt the Olympics.

Dilxat Raxit, spokesman for the exiled World Uighur Congress, says that there was a heavier police presence in Hetian, Kashgar and other parts of Xinjiang.

"Now, if you are a group of more than three or four, you can't congregate together," he said by telephone.

Residents contacted in Lhasa said the city was under tight police watch ahead of a Monday midnight deadline for protesters to give themselves up. Qiangba Puncog said calm was returning.

Foreign reporters are barred from travelling to Tibet without official permission and tourists have been asked to leave.

A Reuters reporter in Sichuan said he saw columns of trucks filled with armed troops on the roads.

In the Aba region, two ethnic Tibetans said hundreds of People's Liberation Army vehicles moved in overnight after unrest in which police said a crowd of protesters had hurled petrol bombs, torching a police station and a market.

"They've been driving through all night. It's just tailing off now," the man said.

In Machu in the province of Gansu, a crowd of 300-400 carried pictures of the Dalai Lama as they marched on government buildings, breaking windows and doors and setting fire to Chinese shops and businesses, the Free Tibet Campaign said.

The London-based group said 100 Tibetan students staged a sit-in at a university in Gansu's capital, Lanzhou, a worry for a country with a history of student unrest, notably the Tiananmen Square protests of 1989 that ended in a military crackdown.

"If the Tibetans in Lhasa take to the streets again in large numbers and really challenge the Chinese authorities, I think we'll see a very harsh crackdown," said Kenneth Lieberthal, a political scientist at University of Michigan.

Speaking from his home in India's Himalayan foothills on Sunday, the Dalai Lama called for an investigation into what he called cultural genocide in Tibet.

Xinhua news agency quoted Tibetan officials as saying the Nobel peace laureate's charge was "downright nonsense" and trumpeted China's development policies in Tibet. Critics say those policies favour Han Chinese migration to the region, contributing to a huge wealth gap between Chinese and Tibetans.