The Chinese doctor who exposed Beijing's Sars cover-up last year is undergoing "brainwashing sessions" in custody, according to media reports.
Many Chinese see Jiang as a national hero for speaking out
Jiang Yanyong is being interrogated about his letter denouncing the 1989 Tiananmen Square crackdown, said sources quoted by the Washington Post.
The authorities have said Mr Jiang, 72, will be held until he "changes his thinking", the newspaper said.
Mr Jiang was detained on 1 June - days before the 15th Tiananmen anniversary.
His wife, Hua Zhongwei, was also taken into custody and went on hunger strike. She was released on 15 June and told not to speak to reporters.
It is not uncommon for China to subject dissidents to "re-education classes" to force them to develop a politically correct mentality, analysts say.
Mr Jiang - a doctor in China's People's Liberation Army - is being held under 24-hour supervision at an undisclosed location, the Washington Post said.
The 1989 Tiananmen crackdown shocked the world
The authorities have threatened to keep him in custody until he "raises his level of understanding" about the crackdown on the student-led rallies for democracy on the Tiananmen Square, it said, quoting one of the sources familiar with the situation.
Mr Jiang - whose February letter urged China's Communist party to reconsider its treatment of the pro-democracy students - has reportedly refused to back down.
He said he would continue to "face the problems confronting me with the principle of seeking truth from facts," the newspaper said, citing a person close to Mr Jiang's family.
In response to the Washington Post questions, the Chinese government said in a statement: "Jiang Yanyong, as a soldier, recently violated the relevant discipline of the military."
"Based on relevant regulations, the military has been helping and educating him," the statement added.
Mr Jiang's family said they had not heard from him in more than a month, apart from a single handwritten note, the UK's Times newspaper reported.
"We are very concerned and have no idea when or if he will come back," a family member told the newspaper.
Mr Jiang became a hero to many Chinese after in March 2003 he exposed the real extent of the Sars (Severe Acute Respiratory Syndrome) epidemic by questioning official statements that had played down the crisis.
His actions led to the sacking of China's health minister and of the Beijing mayor.
Despite the political stand-off with the government, Mr Jiang soon became a celebrity.
And in an apparent U-turn later that year, his face appeared on the front pages of state-run media who praised Mr Jiang's moral courage.