BEIJING (AP) — A veteran journalist who was among prominent intellectuals jailed during China's 1989 Tiananmen Square crackdown has been detained just weeks ahead of the 25th anniversary of the bloodshed on accusations of leaking state secrets.

Police in Beijing detained the influential independent journalist Gao Yu, 70, for illegally obtaining a secret Communist Party document and providing it to a website for publication, the official Xinhua News Agency said Thursday. An investigation was continuing.

State media did not identify the document, but it appeared to refer to reports outside the mainland last year about a high-level, internal circular seen as outlining the party's strategy of attacking Western democratic ideals and crushing dissent to protect its rule.

The strategy paper — known as Document No. 9 — was seen by political observers as early and significant evidence of the hard-line political stance of the leadership of Xi Jinping, who was appointed party chief in late 2012.

Gao, who previously has been imprisoned on state secrets charges, is one of the best-known intellectuals to have been jailed for supporting the Tiananmen pro-democracy protests of 1989. Her latest detention comes amid a clampdown on activists ahead of the politically sensitive anniversary of the June 4, 1989, bloody military suppression of the protesters that killed hundreds, maybe more.

Gao was arrested during the 1989 crackdown and imprisoned for more than a year, and her disappearance late last month was perceived by many observers as likely related to the government's ever-expanding restrictions on people who might want to mark the anniversary.

"Gao Yu is an iconic figure with a special association with the June 4 incident, so we could also interpret it in that respect," said Chinese historian and political commentator Zhang Lifan.

"This is an intimidation tactic," said Willy Lam, an expert on Chinese politics at the Chinese University of Hong Kong. "This is Xi Jinping's way to enforce order and prevent people from speaking ill of the regime."

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Xinhua said Gao was detained April 24, that authorities seized evidence at her Beijing home and that she had confessed to the alleged offense.

State broadcaster CCTV showed a woman identified as Gao, wearing an orange vest over a grey detainee's uniform, walking along a hallway escorted by two police officers to a room where she appeared to be questioned.

Gao's face was blurred out in the footage, but she was heard expressing contrition. "I think what I did touched on the law and endangered the interests of the nation. This was very wrong," Gao said. "I have sincerely learned my lesson and also wish to admit guilt."

The television confession was the latest example of a new tactic used by Chinese authorities in a hard-line campaign against information it deems harmful to party interests. Legal and journalism scholars have said such airing of confessions before court trials undermines the legal process.

Gao, presumably in police custody, could not be reached on her mobile phone, which was turned off. Calls to her home rang unanswered. Beijing police did not immediately respond to a faxed list of questions.

Xinhua did not detail the authorities' accusations against Gao but said she had provided a "secret central party document" to a website outside the mainland, which published it in full in August.

The Hong Kong-based magazine Mirror Monthly published what became known as Document No. 9, exclusively, on its website last August.

At the time, Gao told the Associated Press in an interview that she saw the document as detailing the party's vision of pushing economic reforms in China but preventing challenges to one-party rule.

The reported document argued for aggressively curbing the spread of notions of western democracy, universal values, civil society, freedom of press, and other ideological concepts the party believed threatened its legitimacy.

Human Rights Watch Asia researcher Maya Wang said Gao's detention raised concerns about the authorities' use of state secrets charges against government critics.

"The case highlights the dangerously vague Chinese state secrets law, in which the designation of state secrets is broad and ill-defined, and can't be legally challenged in courts," Wang said.

Gao had previously been convicted of leaking state secrets in 1994 in a secret trial and sentenced to six years in prison, of which she served more than five before being released on medical parole. At the time, the charge was apparently related to her writing about Communist Party politics for a Hong Kong magazine.

The televised confession Thursday was unusual because Gao previously had refused to make any confessions during her previous imprisonment despite being offered early medical parole in return.

Several other well-known dissidents were taken away by police earlier this week, including the prominent lawyer Pu Zhiqiang and at least three other people who had attended a seminar in Beijing to discuss the Tiananmen Square crackdown, a topic that remains taboo.

The U.S. government was "deeply concerned" about the detentions following their "meeting to peacefully mark the upcoming June 4th anniversary of the violent suppression of demonstrations in and around Beijing's Tiananmen Square, " U.S. State Department spokesman Jen Psaki said in Washington.

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Associated Press writers Jack Chang and Didi Tang contributed to this report.