China will next week hold the trial of Xu Zhiyong, a long-time campaigner for legal-reform, prosecuted as part of what is seen as a government-led crackdown on dissent, his lawyer said Friday.

The announcement came as the European Union's outgoing ambassador to China criticised growing curbs on human rights in the country, raising several individual cases including Xu's and a Uighur academic who was detained this week.

Xu -- one of more than two dozen members of the loosely-connected "New Citizens Movement" detained after they called publically for Chinese officials to disclose their assets -- will stand criminal trial on January 22 in Beijing, his lawyer Zhang Qingfang said.

Zhang said Xu, who faces a potential five-year jail term on a charge of "assembling a crowd to disrupt order in a public place," will remain silent during his trial, as will his lawyers, in protest at what they see as the unjust way the court has handled his case.

"It cannot be a just trial," he said, adding: "We can only use silence to express our attitude."

Xu, 40, was detained in July after involvement in peaceful street-demonstrations in which activists held banners calling for asset declaration by government officials, seen by some as a reform which would combat endemic corruption in the country's political system.

The activists formed a loose-knit group referred to as the New Citizens Movement. Members and rights groups estimate that between 20 and 40 people connected with the protests have been detained.

Deteriorating human rights record

Markus Ederer, in his farewell press conference as EU envoy to Beijing on Friday, said Brussels was "concerned on the overall tightening of the human rights situation and especially about the trials of members of the New Citizens Movement, in particular Xu Zhiyong."

He also raised the case of Ilham Tohti, an academic who has criticised government policy towards his mostly Muslim ethnic minority, who are concentrated in the far western region of Xinjiang.

Tohti and his mother were taken Wednesday to an unknown location by several dozen police who seized their mobile phones and computers, his wife Guzaili Nu'er told AFP. The mother was released on Thursday.

China's foreign ministry said Tohti had been "criminally detained" because he was "under suspicion of committing crimes and violating the law".

Ederer, concluding his term as ambassador to take up a position as German vice foreign minister, said: "I have called on the authorities to treat him in line with Chinese legislation, substantiate the charges, which so far has not happened, inform the family about his whereabouts.

"If these charges cannot be substantiated, release him," he added.

The United States on Thursday said Tohti's detention is "part of a disturbing pattern" of arrests of lawyers, activists, journalists "and others who peacefully challenge official Chinese policies and actions".

Responding to the EU and US criticism over Tohti, China's foreign ministry spokesman Hong Lei said Friday: "We are opposed to any country or party's accusation against any other country's normal enforcement of law under the pretext of human rights.

"We are also opposed to their interference in other countries' domestic affairs and judicial sovereignty."

Ederer also cited Liu Xia, the wife of jailed Nobel laureate Liu Xiaobo, who has never been charged with any crime but has been under house arrest for years.

Chinese authorities have largely restricted Liu Xia to her Beijing home since 2010 when her already imprisoned husband -- an outspoken advocate of democratic reform -- was awarded the Nobel peace prize.

"We remain concerned about Liu Xia's house arrest," Ederer said.