China sentenced lawyer and prominent rights activist Guo Feixiong to a prison term of eight years on Thursday, with diplomats from several countries saying they were barred from the trial in the southern city of Guangzhou.

The sentence follows terms of more than a decade in jail each handed to two prominent rights lawyers, Ding Jiaxi and Xu Zhiyong in April, amid China's clampdown on dissent since President Xi Jinping came to power in 2012.

While rights groups say hundreds of lawyers and activists have been detained in recent years, China says it respects the rule of law and individual rights and rejects criticism of its human rights record.

Guo, 58, has drawn international attention for campaigns against issues such as graft and censorship, and his accusations of mistreatment by Chinese authorities during more than a decade behind bars on previous charges.

His latest detention, in 2022, came a year after he was stopped from leaving the country to visit his dying wife in the United States, sparking further outcry.

After a three-hour trial Guo, whose real name is Yang Maodong, was found guilty of defaming China's political system and inciting subversion of state power, his brother said in a statement, adding that Guo would appeal against the judgment.

Thursday's statement was confirmed by Guo's lawyer.

Diplomats from several countries said they were prevented from attending the trial.

"Today, U.S. diplomats were blocked from attending the court proceedings of Guo Feixiong," the U.S. embassy in China said on its Twitter account. "We continue to call for Mr. Guo's speedy release so he may be reunited with his family."

Diplomats from Britain, Canada, Denmark, France, Germany, and the Netherlands were also turned away and told by a court clerk that foreign visitors needed approval from higher authorities, four diplomats told Reuters on condition of anonymity.

The Guangzhou Intermediate People's Court and China's foreign ministry did not immediately respond to requests for comment.

In early 2021, Guo was stopped by officials at the airport in the commercial hub of Shanghai as he sought to visit his ailing wife in the United States.

His public pleas to be allowed to leave were rebuffed and his wife died of cancer about a year later. Two days after that, Guo was arrested by Guangzhou police and has been held in detention since, according to rights groups.

Guo was subjected to "years of mistreatment, imprisonment, routine harassment and surveillance, and denied foreign travel for his peaceful advocacy on behalf of the Chinese people," the U.S. state department has said earlier.