Video footage from Tibet is extremely rare. The film, which shows violent scenes from the March 2008 riots, is the clearest evidence yet that Tibetans were subject to police brutality as China struggled for control in Lhasa.
In the seven-minute film, […] Chinese police kick and beat apparently defenceless Tibetan protesters and monks after they have been handcuffed and are lying on the ground.
The Tibetan government-in-exile, which is based in Dharamsala in India, said the treatment of the captives violated international norms and amounted to torture.
Until now, the only video evidence of the riots in March  was shot from long-distance and showed clashes in the streets of Lhasa but not evidence of torture.
"This is the first footage which visibly proves the use of brutal and excessive force against Tibetan protesters. It clearly challenges official Chinese statements that disproportionate force was not used on unarmed protesters," said Stephanie Brigden, the director of the international campaign group Free Tibet.
The second half of the video, […] documents a serious set of injuries allegedly sustained by a Tibetan worker after he intervened in the beating of a monk.
According to the Tibetan government-in-exile, Chinese police shot at the man, who was named as Tendar, and then stubbed cigarettes out on his body, forced a nail through his right foot and beat him with an electric baton.
He was initially taken to a military hospital but, according to the video, his wounds were merely wrapped in cling film, which allowed them to rot. He subsequently died of his injuries in June 2008.
The video was shot as the riots spread from Lhasa to the rest of Tibet and into the surrounding provinces of Qinghai and Gansu in March of last year. With the Olympic Games helping to focus international attention on China, the authorities launched a heavy-handed response to try to snuff out dissent.
China has repeatedly denied any brutality in Tibet and angrily rejected a call from the United Nations last November  to clarify the measures it took in the wake of the riots in March . It accused the UN of "prejudice against China" and of fabricating evidence to "deliberately politicise the issue".
But the Tibetan government-in-exile has said that Chinese troops killed 220 Tibetans and injured almost 1,300 during the protests. It has claimed that 5,600 Tibetans were arrested, and more than 1,000 have "simply disappeared". Beijing has said that only 22 people died in the rioting.
The Tibetan government-in-exile compared the new footage to a video of Chinese police beating monks at the Jokhang temple in 1988, which was the first time that Chinese brutality was captured on film.
The anniversary of last year's riots  apparently passed by peacefully last week, as China poured police onto the streets of Lhasa to ensure control. But all foreigners have been banned from Tibet and from large swathes of the surrounding provinces in order to close the region to outside eyes.
In Amdo, the north-eastern Tibetan state, human rights activists reported that more than 100 monks had been taken away for "re-education" from the Lutsang monastery in the run-up to the 50th anniversary of the Dalai Lama's exile from Tibet last week [March 2009].
Police are still checking cars on roads leading to Tibet and motorway toll booths outside Chengdu, in Sichuan, are manned with heavily-armed officers.
Chengdu is often used as a starting point to journey to Tibet and security is particularly tight there. Video cameras have been installed in taxis and all taxi drivers are required to report any foreigners to the authorities.