The reports coincided with a visit by a group of diplomats, who were led on a closely guarded tour of the city that has been at the heart of unrest throughout China's ethnic Tibetan regions just months before the opening of the Beijing Olympics.

'We don't know how many people, but it seems it's quite a lot of people,' Mr Tenzin Taklha, a spokesman for Tibet's exiled spiritual leader, the Dalai Lama, said of the events in Lhasa.

'I think it's timed with the visit of the diplomats.'

The Dalai Lama has urged the 'world community' to help end the turmoil in his homeland, after global leaders renewed calls for talks between him and China.

Hours before his comments, the foreign diplomats from 15 embassies - including those of the United States, Britain, France and Japan - arrived in Lhasa.

They had demanded unfettered access to Lhasa, where deadly riots first broke out more than two weeks ago.

Last week, foreign reporters were allowed into the city in a visit orchestrated by the authorities. Beijing blames the unrest on the Dalai Lama and his supporters.

Yesterday, the spiritual leader told a news conference in New Delhi that he was 'helpless'.

'We have no power except justice, truth, sincerity...that is why I appeal to the world community to please help,' he said. 'My side is open...we are waiting.'

The Dalai Lama also said the ever-increasing numbers of non-Tibetan Chinese moving into his troubled homeland threatened to stifle Tibet.

'There is demographic aggression,' he said, calling the population shift a 'form of cultural genocide'.

US President George W. Bush on Friday publicly pressed China to hold talks with representatives of the spiritual leader.

The Dalai Lama, who claimed to advocate non-violence in seeking liberation of Tibet, reiterated that he was 'fully committed' to China hosting the Olympics in August.

But the 72-year-old added it was important 'to remind the Chinese that in order to be respected hosts of the Games', human rights in Tibet must improve.

Reuters, AP, AFP