By Michael Bristow
BBC News, Beijing
Unverified video of Tibetan monks being assaulted posted on YouTube
China says video footage that purportedly shows Chinese security personnel violently beating Tibetans last year is "a lie".
The video apparently shows protesters being beaten with sticks, and kicked and choked by China's security forces.
The Tibetan government-in-exile says the footage shows China's "brutality".
But a Chinese government official said many of the images and voices in the video had been pieced together from different sources.
The video-sharing site YouTube has recently been blocked in China, which could be because the site had been carrying the contentious video.
The footage was released by the Central Tibetan Administration, Tibet's government-in-exile, last week, and cannot be independently verified.
But Tseten Samdup Chhoekyapa, the Dalai Lama's representative, said the footage showed "police beating protesters".
"The footage clearly shows the beating of Tibetan captives even after they are handcuffed and tied, a violation of international norms," said the representative.
The government-in-exile also said the footage featured a Tibetan called Tendar, who died after being beaten by the Chinese security forces.
It said Tendar was on his way to his office when he was beaten while trying to stop Chinese police officers hitting a monk.
Some of the footage was shot in or near Lhasa after riots and protests erupted throughout Tibetan areas in March last year, according to exiled Tibetans.
During the unrest last year Chinese state-run television released its own footage of Tibetans, including monks, rioting in Lhasa.
But Tibetan exiles say this is the first time there has been footage that shows Tibetans being beaten by the Chinese security forces.
In its first response to the video's release, an unnamed government official from China's Tibetan Autonomous Region said it was a lie.
He was speaking to the official Xinhua News Agency in a report that was released late on Tuesday.
"Technology experts found that video and audio was edited to piece together different places, times and people," Xinhua said, quoting the official.
China also rejected the claims about Tendar.
"Tendar died from a disease at home awaiting court trial," the official said, adding that he had used a knife to "slash" a policeman.
The official added that the injured person in the video was not Tendar and the wounds were fake.
"The Dalai Lama group is used to fabricating lies to deceive the international community, and the aim of this video is to hide the truth of the 14 March riot," Xinhua quoted the official as saying.
The Tibetan government-in-exile says that about 220 Tibetans were killed and nearly 1,300 seriously injured following the unrest last year.
The Chinese government says at least 18 civilians and one policeman were killed, mostly in riots in Lhasa on 14 March.