Pu appeared Sunday before the 2nd Beijing Intermediate People's Court in a case that international rights groups have criticized as political persecution.

He is a public figure in China and was instrumental in pushing for the eventual abolishment of the labor camp system, which allowed police to jail people for up to four years without a trial.

"Pu's trial is extremely important - he's the ultimate canary in the coal mine," Maya Wang, a China researcher for Human Rights Watch said. "If they decide to be harsh against him, I'd say it'll signify a further escalation of hostility towards human rights activism."

His case revolves around a number of posts on China's Twitter-like Sina Weibo that questioned the ruling Communist Party's policies toward the Tibetan and Uighur ethnic minorities in the Tibet and Xinjiang regions, and mocked political figures.

If convicted, Pu faces up to eight years in prison.

Police forcefully barred observers - including diplomats, journalists and supporters - from entering the courtroom. Some 40 well-wishers gathered outside the courthouse and chanted slogans to show solidarity with the accused.

"Pu Zhiqiang is not a criminal. He will be judged by history," Qu Biao, a 53-year-old teacher from the northern Shaanxi province, told the Reuters news agency. "The Chinese constitution protects freedom of speech, so putting him on trial is unjust and shameless. If Pu Zhiqiang is guilty, then we are all guilty."

A woman is caught in a scuffle on a spring day in 1989. Later that night, the 38th army would open fire on unarmed civilians in one of the bloodiest crackdowns of the 20th century

Arrested at illegal commemoration of 1989 Tiananmen Square massacre

China routinely prosecutes activists and dissidents under a law forbidding "picking quarrels and provoking trouble" and dismisses any criticism of its rights record.

Beijing has launched a crackdown on online rumors over the past two years, detained hundreds of human rights lawyers in a nationwide sweep and jailed a reporter on a charge of leaking state secrets.

The 50-year-old attorney was taken into custody in May 2014 after he attended a meeting in a private home to commemorate the bloody 1989 crackdown on pro-democracy protesters on the capital's Tiananmen Square. Pu, who had participated in the protests, had vowed to commemorate the anniversary every year in memory of the hundreds killed by security services.

jar/gsw (AP, Reuters)