(CNN) -- Prominent Chinese journalist and press freedom advocate Gao Yu has been detained for allegedly leaking state secrets, China's state-run news agency Xinhua reported Thursday.
The detention puts Gao on a growing list of dissident voices and intellectuals who are being held by police ahead of the 25th anniversary of the Tiananmen Square crackdown.
The 70-year-old is accused of sharing a "highly confidential document" with a foreign website that published the material last year. The document, issued by the Communist Party's Central Committee, was widely distributed online, according to the report.
Xinhua did not specify which document was leaked and did not name the website that published it.
After she was detained, Gao expressed "deep remorse" for her actions, according to Xinhua. She told police in Beijing she "deeply regretted that her behavior harmed the nation's interests and violated the law, and she is willing to accept punishment from the law," according to the report.
Chinese broadcaster CCTV televised Gao's confession on Thursday morning.
Police arrested Gao on April 24 and seized evidence from her home in the Chinese capital, according to Xinhua.
Other high-profile activists and scholars have been detained in recent weeks, including human rights lawyer Pu Zhiqiang and four other people who attended a low-key event last week marking the 25th anniversary of the June 4th Tiananmen Square protests.
Gao was reported missing after she failed to attend the meeting.
The outspoken journalist, whose columns are published on German news outlet Deutsche Welle's Chinese-language site, began her career as a reporter for the China News Service in 1979.
She was arrested after the Tiananmen Square protests in 1989 and released more than a year later. She was imprisoned for another six years for leaking state secrets in 1993.
CNN's Zhang Dayu and Beijing intern Andi Wang contributed to this report.