A Tibetan activist has gone on trial in China for separatism, after he spoke to the New York Times about his efforts to preserve the Tibetan language.

Tashi Wangchuk pleaded not guilty on Tuesday, in a trial rights groups have called “ludicrously unjust”.

The 32-year-old has been in detention since January 2016, shortly after he appeared in the New York Times documentary.

His lawyers say he could face up to 15 years in jail if found guilty.

In the video, Mr Tashi said Tibetan culture was being destroyed in China.

He attempted to file a lawsuit in Beijing against local officials in his hometown, Yushu, saying they were sidelining the Tibetan language in favour of Mandarin in schools.

The documentary was used as a key piece of evidence by the prosecution, Mr Tashi’s lawyer, Liang Xiaojun, told reporters.

“He doesn’t believe he’s incited separatism,” Mr Liang said. “He only wants to strengthen Tibetan language education.”

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A New York Times spokesman said: “This action by the Chinese government sends a chilling message meant to silence its critics.”

Roseann Rife, Amnesty International’s East Asia Research Director, said: “It is appalling that Tashi Wangchuk could face up to 15 years’ imprisonment simply for expressing his views in media interviews.”

Tibet, a remote and mainly Buddhist territory known as the “roof of the world”, is governed as an autonomous region of China.

Beijing says Tibet has developed considerably under its rule. But rights groups say China continues to violate human rights, accusing Beijing of political and religious repression – something Beijing denies.