Security forces have poured in to several regions
China has admitted for the first time that anti-Beijing protests have spread outside the Tibetan Autonomous Region, as security is ratcheted up.
Xinhua news agency reported huge damage to government buildings and shops after riots in Sichuan province on Sunday.
And officials said 24 people had been arrested after demos in the Tibetan city of Lhasa, and 170 protesters had surrendered to authorities.
Hundreds of troops have been seen pouring into Tibetan areas.
On Wednesday alone, BBC reporters saw more than 400 troop carriers and other vehicles on the main road - the largest mobilisation witnessed since the unrest began.
And the authorities have placed strict limits on Western journalists trying to report on the unrest.
Georg Blume, a German journalist who was forced out of Lhasa on Thursday, said security forces had told him he was the last foreign journalist in the city.
He told the BBC that police were "everywhere" and he had seen them going into houses and carrying out searches.
Tibet's spiritual leader the Dalai Lama has reiterated his willingness to meet Chinese President Hu Jintao - if he receives "concrete indications" of what the Chinese can offer.
But senior Chinese officials have repeatedly accused him of orchestrating the protests from his base in the Indian town of Dharamsala, and the foreign ministry once again labelled him a "splittist" on Thursday.
Meanwhile, the BBC has obtained dramatic footage filmed by the security forces of some of the first clashes between monks and the military last week.
Chinese and Tibetan sources have given very different accounts of the protests that began in Lhasa on 10 March, on the anniversary of a Tibetan uprising against Chinese rule.
Xinhua, which is state-run, has published graphic articles describing the violence it blames on rioters, saying 13 people were stabbed or burnt to death in unrest in Lhasa.
The agency referred to protesters in Aba country, Sichuan, as "mobsters", saying they had caused "great damage" to shops and government offices.
Tibetan exiles say that at least 99 people have died so far, including 80 in Lhasa - and accuse security forces of firing on crowds.
State media reported that 170 people had now handed themselves in - up from the 105 people they said had surrendered to police in Lhasa.
The authorities had threatened "harsh punishments" for those who failed to meet a Monday deadline.
China says Tibet was always part of its territory
Tibet enjoyed long periods of autonomy before 20th century
1950: China launched a military assault
Opposition to Chinese rule led to a bloody uprising in 1959
Tibet's spiritual leader the Dalai Lama fled to India
On Thursday the state-run Tibet Daily quoted prosecutors as saying that two dozen suspects had been arrested for "endangering national security as well as beating, smashing, looting, arson and other grave crimes".
Demonstrators had called for Tibetan independence and waved the flags of Tibet's "government-in-exile", it said.
It was not clear whether the 24 arrested were among the 170 reported to have surrendered. Rights groups say they have heard reports that hundreds had been arrested.
UK Prime Minister Gordon Brown said China's Premier Wen Jiabao had told him he was open to talks under certain conditions.
He said he had told Mr Wen that he would meet the Dalai Lama during a visit to London in May and that the violence in Tibet must end.