The findings were contained in a 12-page document that was first reported on Friday by The Guardian. They have not been publicly released, but United Nations officials in Geneva confirmed the document’s authenticity.
The findings represent a sharp rebuke of China’s treatment of the activists that will be all the more unwelcome to Beijing, as it coincides with a weeklong Communist Party congress setting China’s course for the next five years — an event minutely choreographed to avoid any signs of dissent or disaffection.
The men were arrested as part of a widespread crackdown on human rights activists — and the lawyers representing them — that President Xi Jinping unleashed in 2015. Hundreds of people have been questioned and detained as part of the crackdown.
Mr. Xie, a 45-year-old lawyer who had defended mainland supporters of Hong Kong pro-democracy protests, was arrested in July 2015 and held in isolation in a secret detention center. In transcripts of meetings with his lawyers, which they released in January, Mr. Xie told of torture and abuse inflicted by interrogators, who threatened to turn him into an “invalid” unless he confessed.
Mr. Xie was put on trial in May for inciting subversion of state power and disrupting court order. In a video released by the court, he denied being mistreated and said his actions “go against my role as a lawyer.” The court released him on bail.
Mr. Hu, 62, an outspoken advocate of religious freedom and democracy who led several underground churches and had already served a 16-year prison term, was sentenced last year to seven and half years in prison.
Mr. Zhou, 52, described by prosecutors as a radical who conspired with foreign governments and rights groups to take on cases that undermined the Communist Party, was sentenced last year to seven years in prison. Mr. Zhou had led a firm of a hundred lawyers that handled numerous cases deemed sensitive by the authorities, representing the dissident artist Ai Weiwei, members of the banned Falun Gong movement and the victims of a contaminated baby formula scandal in 2008.
The United Nations panel weighed the Chinese government’s charges against the accounts by people acting on their behalf and concluded they had been arrested “because of their work to promote and protect human rights.”
The panel said it was convinced the three men had not enjoyed their legal rights to due process, including access to lawyers, and said it was deeply concerned by allegations of torture. The panel also said it was not convinced by government claims they had confessed, observing that the government had not responded in “an explicit and comprehensive manner” to allegations they were obtained under torture.
The panel’s findings represented “a very serious, methodical effort to understand the facts of these cases” and called into question the government’s arguments that human rights defenders are subversives trying to undermine the state, Sophie Richardson, the China director at Human Rights Watch said.
The panel opinion released on Friday was the latest in multiple interventions over cases of arbitrary detention in China. In the past it called for the release of the prominent intellectual Liu Xiaobo, who died in detention in July, and for release of his wife, Liu Xia.
In April it called for the release of a prominent Tibetan activist Tsegon Gyal, detained in December on charges of “inciting to split the country” and in May it said authorities should release three activists — Huang Wenxun, Yuan Bing and Yuan Xiaohua — who were arrested in May 2013.
The panel’s findings underscored the critical value of such United Nations human rights mechanisms, Ms. Richardson said in phone interview. “To have these bodies able to render these kind of investigations and decisions is extraordinarily important,” she said. “It is to these bodies that people inside China can reach out for some kind of redress because they aren’t going to get it at home.”