BEIJING — A court in southwestern China has handed an unusually heavy punishment — 12 years in prison — to one of the country’s most prominent activists despite appeals for clemency from international rights organizations and U.N. experts.

Huang Qi, 56, was sentenced for “deliberately disclosing state secrets” to foreign parties, the Mianyang Intermediate People’s Court in Sichuan province said in a brief online announcement Monday. Huang is the founder of the website 64 Tianwang, which aired accounts of government abuse, corruption and fecklessness from across China for two decades.

Before his most recent arrest, in 2016, Huang had served two stints in prison for his advocacy and spent roughly half of the past 20 years behind bars. Each time he was released, he returned to publishing his website, which became a go-to destination for Chinese petitioners who had few options to seek redress for abusive working conditions or land grabs.

Huang was best known for campaigning on behalf of parents whose children were crushed in shoddy buildings that collapsed during the 2008 Sichuan earthquake, which left more than 80,000 people dead or missing and created a political crisis for the Communist Party.

Huang’s work would inspire members of China’s “weiquan” — or rights defense — movement to use the Internet to circumvent traditional news outlets and to name and shame officials on issues, which infuriated the government.

Huang, who is suffering from a serious kidney ailment, will be released in late 2028 if he serves his full term.

Cédric Alviani of Reporters Without Borders, which awarded Huang its Freedom Prize in 2004 and 2016, said Monday that Huang’s 12-year term is “equivalent to a death sentence, considering Huang Qi’s health has already deteriorated from a decade spent in harsh confinement.”

More than a dozen international human rights groups have called on China to release Huang. His 85-year-old mother, Pu Wen­qing, traveled from Sichuan to Beijing in late 2018 to appeal to judicial authorities for his release, citing his deteriorating kidney. She was trailed by state security agents and later disappeared for weeks.

Reached by telephone at home in Sichuan, Pu told The Washington Post on Monday that she is under house arrest, with guards posted inside her home and outside her apartment door. She said she had not been notified of Huang’s sentence and declined to comment further.

Since 2015, hundreds of Chinese activists have been detained, and dozens have been prosecuted on subversion charges in a nationwide crackdown. Many were quickly released; some were given relatively light sentences after they admitted guilt. Others faced longer terms because they refused to adequately cooperate or provide confessions.

Huang’s sentencing, three years after his arrest, was perhaps meant to send a tough message about a figure seen as a dogged icon for China’s dwindling circle of dissidents — and an intolerable gadfly to authorities.

One of Huang’s confidants, who spoke on the condition of anonymity for fear of reprisal by authorities, said Huang unleashed a courtroom diatribe about President Xi Jinping during his closed-door trial this year and clashed with court stenographers who refused to record his remarks.

“It was his attitude,” said Patrick Poon, a China researcher at Amnesty International, which has called for Huang's release. “Huang would not admit to any offenses. They were giving a lot of pressure to him and his family, but he refused to concede.”

In December, the U.N. Working Group on Arbitrary Detention called on China to release Huang, noting his poor health and allegations of mistreatment behind bars.

The government said in response that Huang’s illness was “under control” and dismissed allegations of torture as “inconsistent with the facts.”