Explosives and Anger on Eve of 50th Anniversary of Dalai Lama's Exile

President Hu Jintao yesterday called for a "great wall" of stability in Tibet on the eve of the 50th anniversary of the failed anti-Chinese uprising which led to the Dalai Lama's flight into exile.

Angry crowds had earlier hurled home-made explosives in a Tibetan area of Qinghai province, damaging police cars, state media reported.

The unrest broke out after police stopped a truck at a checkpoint amid a security lock down across Tibet and areas of western China with large Tibetan communities. It is not known who threw the devices, which are fairly common in China.

This month is doubly sensitive, given last year's riots in Lhasa and the subsequent wave of disturbances. Increased numbers of armed police are patrolling Tibetan areas and extra troops are guarding Tibet's borders.

In many areas foreigners and journalists have been detained or turned away and mobile phone and internet access has been cut in places.

"We should build a solid great wall to oppose the separatists, uphold the unity of the motherland and advance Tibet from basic stability to lasting stability," Hu said in comments played on state television. He served as the Communist party secretary in the region during protests in 1989.

Anti-Chinese riots exploded in Lhasa last March, apparently after peaceful protests to mark the 1959 rebellion were suppressed. Officials say that 22 people, mostly Chinese, were killed, while the Tibetan government in exile claims that scores died in the crackdown which ensued as unrest rippled across Tibetan areas.

Human rights and exile groups said yesterday that hundreds of people detained during the disturbances were still unaccounted for.

Kang Jinzhong, Communist party commissar of the people's armed police in Tibet, told the state news agency Xinhua that he expected no unrest but anti-riot forces were ready.

A senior border official said that China had also deployed troops to strengthen controls along the mountain frontier between Tibet and south Asia.

The Dalai Lama warned last week that violence could break out in the region at any time. He had earlier told followers that the authorities were trying to provoke them to justify an "unimaginable forceful clampdown".

The Chinese accuse him of attempting to split the country, but the Tibetan spiritual leader says he seeks autonomy rather than independence and denies Chinese allegations of fomenting unrest.

The International Campaign for Tibet claimed yesterday that more than 1,200 Tibetans were still missing following last year's unrest, and Amnesty International put the figure as high as 1,400. Both cited accounts by people detained but then released, as evidence of beatings and other abuse in custody.

The Chinese foreign ministry and public security ministry did not immediately respond. Officials said this weekend that 76 of the 953 people detained for their involvement in the Lhasa riot had been given prison sentences, mostly for offenses such as arson, and the rest had been released.

But Human Rights Watch said that in November last year a senior official in the region said 1,317 people had been detained.

The group also said that authorities in Gannan in Gansu province reported that they had detained 432 protesters, accepted the "voluntary surrenders" of 2,224 people, and released 1,870. It is not known what subsequently happened to the 334 people not released, who included 106 monks.

Similarly, nothing is known of 670 people said to have voluntarily surrendered in Sichuan province.

"The Chinese government has refused every external request for a real accounting of the detention, arrest and sentencing of those involved with the Tibetan protests," said Sophie Richardson, the group's Asia advocacy director.

Prof Robert Barnett, an expert on Tibet at Columbia University in New York, said that China's crackdown following last year's riot had made the anniversary more sensitive. "A year ago I think it would have been important to a certain category of people in Tibet ... people deeply unhappy with the trend of Chinese policy. But that group will now have been magnified many times over by the decisions of the last year and the whole of China's history in Tibet is now in front of people's eyes. They will be asking questions about whether it has been worthwhile," he said.