Pu's microblog messages contained sarcastic criticisms of the party and its policies towards ethnic minorities and neighbouring countries.

His associates say his sharp criticisms of the government, his representations of many high-profile rights cases and his popularity in the Chinese media has rendered him a threat in the eyes of the authorities.

The party-controlled judiciary would likely find Pu guilty to make an example of him as a way to warn other rights advocates, they said.

The US Embassy in Beijing issued a statement this morning calling for the Chinese authorities to release Pu.

“Lawyers and civil society leaders such as Mr. Pu should not be subject to continuing repression, but should be allowed to contribute to the building of a prosperous and stable China,” the statement read. “We urge Chinese authorities to release Mr. Pu, and call upon China to uphold fundamental civil rights and fair trial guarantees.”

Pu’s indictment in May centred on 30 microblog postings made between 2011 and last year, but the list was narrowed down to the content of seven texts at a pretrial meeting in a Beijing court last week. The commentaries were mostly remarks critical of the government’s handling of an ethnic conflict in Kunming, Yunnan province, last year and sarcastic comments about two officials.

Last week, Pu told his lawyer that his online remarks were “emotionally charged, sarcastic and even rude sometimes”, but insisted that he had done nothing to warrant the charges against him.

Pu, who suffers chronic illnesses including diabetes, heart disease and high blood pressure, has been detained for 19 months without trial. Human Rights Watch says his treatment “is disturbingly typical of those who try to use peaceful means to challenge injustices by the state”. Requests for bail have been rejected by the court.

Pu, 50, a charismatic, burly figure with a deep, sonorous voice, has defended artist Ai Weiwei and other prominent rights activists, advocating the scrapping of the country’s labour camp system and more recently, aided Communist Party members that had been tortured during corruption investigations.

A photograph taken during the 1989 Tiananmen Square pro-democracy movement depicts Pu, who was a 24-year-old history graduate student at the time, wearing a brown paper vest emblazoned with the slogan - “freedom of the press, freedom of assembly”.

“Thanks to a mysterious twist of fate, this has become my life’s mission,” he said last year, just weeks before he was detained by the police in May.

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Legal scholar Teng Biao, a former colleague of Pu, said his role both as an outspoken human rights lawyer and a government critic plus his popular exposure in the Chinese media have made him a threat in the eyes of the authorities.

“He criticised the authorities, defended human rights cases and had a media platform. These have posed a challenge to the government’s authority,” Teng said.

Many supporters worried about Pu after he posted online criticisms about former security chief Zhou Yongkang in 2013 after he stepped down from power. Before Zhou was investigated for corruption, Pu accused him of violating human rights through his stability-maintenance apparatus.

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Teng said Pu’s trial was the latest in a series of crackdown on lawyers and rights advocates under President Xi Jinping’s rule.

“The growth of the rights defence movement has made the authorities feel threatened,” he said.

Lawyer Zhang Xuezhong said Pu’s sentencing was part of the authorities’ wider security agenda to restrain the development of the rights defence movement. “They see rights lawyers as a threat,” he said.

Amnesty International said Pu’s trial was “an act of political persecution in which the authorities are trying to silence an independent voice”.