China has detained a prominent former journalist for leaking "state secrets", police said Thursday, the latest move to silence critics of the ruling Communist Party ahead of June's 25th anniversary of the Tiananmen Square crackdown.

Gao Yu, 70, was "criminally detained on suspicion of providing state secrets to sources outside China", the Beijing public security department said in a message on its verified microblog Thursday.

Gao, the former deputy editor-in-chief of the magazine Economics Weekly, is a well-known journalist who was named one of the International Press Institute's 50 "world press freedom heroes" in 2000.

Her political writings have seen her jailed in the past. In 1993, she was sentenced to six years in prison on a similar "state secrets" charge.

She was paraded Thursday on state-run China Central Television, in the latest instance of authorities publicly shaming influential critics of Beijing with televised confessions.

It showed her being escorted down a hallway and interrogated by two uniformed police officers.

"I believe what I have done has touched on legal issues and has endangered the country's interests," said Gao, whose face was obscured on the broadcast.

"What I have done was a big mistake. I earnestly and sincerely have learned a lesson from this experience and admit my guilt," she said.

Gao had been missing for the past two weeks, and her associates became alarmed when she did not show up at a private Tiananmen-related gathering she had been scheduled to attend.

According to the official news agency Xinhua, Gao was held on April 24 on suspicion of having sent a copy of a "highly confidential" document to an overseas website last June.

Police seized "substantial evidence" from her home and Gao has "expressed deep remorse about what she did", Xinhua said, adding that she was "willing to accept punishment from the law".

The Xinhua report did not name the document that Gao is alleged to have leaked.

But Gao has written previously on "Document No. 9", a Communist Party internal communique calling for a harsh crackdown on dissent and warning against "perils" such as multi-party democracy and universal values.

The document circulated early last year and its full text was published by a Hong Kong-based magazine last August.

- 'Vaguely worded and arbitrary' laws -

Gao's detention comes amid a crackdown on academics, rights activists and other Communist Party critics ahead of the sensitive June 4th anniversary.

Pu Zhiqiang, one of China's most celebrated human rights lawyers, was arrested on Tuesday "over charges of creating disturbances", his lawyer told AFP, and campaigners say others have also been held.

The US is "deeply concerned" over the reports and has called for their immediate release, State Department spokeswoman Jen Psaki said Wednesday.

Sophie Richardson, China director for Human Rights Watch, said that the recent charges and detentions of activists "lay bare just how little the Chinese government's attitudes towards human rights have changed since 1989".

"A stable society is one in which peaceful discussions of history and accountability are tolerated -- not crushed or criminalised," she said in a statement.

Anu Kultalahti, China researcher at Amnesty International, called Gao "the latest victim of China's vaguely worded and arbitrary state secret laws which the authorities repeatedly use as a smokescreen to target activists".

Campaign groups have also expressed alarm over the rise in televised "confessions" in China, which often take place before the accused is granted a trial or access to a lawyer and appear to be an attempt to deter others.

Chinese-American investor Charles Xue, who regularly posted critiques of the Chinese government to his 12 million microblog followers, confessed on CCTV last September that he had used microblogging to "gratify my vanity".

Xue had been arrested the previous month on charges of soliciting prostitutes, and was released on bail in April pending trial.

Another prominent blogger, Pan Shiyi, was shown in an interview with CCTV where he appeared contrite and warned of the dangers of "casual" online posts.