A Chinese human rights lawyer was accused by state media of being the "mastermind" behind a series of "illegal religious gatherings" Thursday, in the latest in a deepening crackdown on lawyers and activists.

Zhang Kai, who represented churches fighting back against the Communist party's campaign to take down crosses, was seized by security officials last August.

He disappeared from the city of Wenzhou, dubbed "China's Jerusalem" for its large Christian population, in the eastern province of Zhejiang, and his whereabouts remained unconfirmed for months.

Citing information from the city's public security bureau, state-run website Wenzhou Online said that Zhang had been identified as the "mastermind" behind a series of "illegal religious gatherings".

It further accused him of "accepting foreign trainings", "encouraging people to confront the government", and cheating people out of money, among other claims.

Under President Xi Jinping, China's ruling Communist party under has reasserted controls over civil society, detaining more than 130 human rights lawyers and legal staff in the past year.

Last week, UN rights chief Zeid Ra'ad Al Hussein called on China to release about 250 detained human rights lawyers, legal assistants, and activists "immediately and without conditions".

The website, which referred to Zhang as a "criminal suspect," also quoted his alleged confession.

"I violated national law, disrupted social order, endangered national security, and violated the professional code of conduct for lawyers," it cited Zhang as saying.

"I also warn those so-called human rights lawyers to take me as a warning and not collude with foreigners, take money from foreign organisations, or be engaged in activities that break the law or harm national security and interests," he continued, according to the report.

China invited international censure after it detained and expelled a Swedish human rights activist Peter Dahlin who had aided Chinese lawyers, after parading him on state television confessing to breaking the law.

While forced public confessions are an old practice in Communist China, there has been a resurgence of such incidents since Xi took power in 2012.

Last month, Reporters Without Borders (RSF) called for the European Union to impose sanctions on Chinese state media, denouncing broadcasts and reports of forced confessions by detainees as "peddling lies" and of "no informational value".