Eleven countries have jointly called on the Chinese government to investigate reports of torture against human rights lawyers and urged Beijing to abandon a controversial detention system that holds suspects in secret locations for months at a time.

The unusually direct criticism comes in a letter from the Chinese diplomatic missions of the signatory countries, including Canada, that expresses "growing concern over recent claims of torture and other cruel, inhuman or degrading treatment or punishment in cases concerning detained human rights lawyers and other human rights defenders."

The signatories call for China to end the practice of "residential surveillance at a designated place," a Chinese form of pretrial custody for sensitive cases that allows suspects to be held for up to six months, often without families or lawyers being told where they are.

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Residential surveillance amounts to "incommunicado detention in secret places, putting detainees at a high risk of torture or ill-treatment," the letter states. China should, it says, remove all suspects from residential surveillance and repeal enabling legislation.

Related: China takes aim at civil society in systematic crackdown: report

"Detaining people without any contact with the outside world for long periods of time is contrary to China's international human rights obligations," the letter says.

It calls for a prompt and independent investigation into "credible claims of torture" against lawyers Xie Yang, Li Heping, Wang Quanzhang and Li Chunfu, as well as activist Wu Gan.

Under Xi Jinping, Chinese authorities have waged what critics have called a war on civil society, detaining and arresting labour activists, women's rights campaigners and human rights defenders. Hundreds of human rights activists and lawyers have been questioned and detained, Amnesty International has said.

Mr. Xie has told his lawyers he was punched, kicked and kneed by interrogators who threatened: "I'm going to torment you until you go insane." Authorities used electric shocks to torture Li Heping and Mr. Wang, their wives were told. Family members of Li Chunfu said 500 days of secret detention left him with a mind that was "shattered." Wu Gan has said he was not allowed to sleep for several days and nights.

The Globe and Mail obtained a copy of the Feb. 27 letter, which has not been made public. It was addressed to Guo Shengkun, China's Minister of Public Security. It was signed by ambassadors and chargés d'affaires from Australia, Canada, Japan and Switzerland, along with seven European Union member countries: Belgium, the Czech Republic, Estonia, France, Germany, Sweden and the United Kingdom.

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Neither China's public security ministry nor its foreign ministry responded to requests for comment on Monday.

"Canada raises human rights with our Chinese counterparts regularly, using a variety of methods," an embassy spokesperson said in a statement. "Sometimes it is public, but often these issues are best raised privately, where we can have a frank discussion." The Japanese embassy declined comment, since the letter was sent through a diplomatic channel. The German embassy said it is "not in a position to comment."

Joint action is often the most effective way to pressure China, human rights advocates say.

"Beijing always hears a clearer and firmer message when it's delivered by multiple governments," said Sophie Richardson, China director for Human Rights Watch. The issuance of joint letters is "a strong indication of the widespread concern about human rights erosions in China today."

Shortly after the letter was sent, Chinese government-controlled media published a week-long series of articles and social media posts lashing out at what People's Daily called "FAKE NEWS" in Western media reports on the torture of Mr. Xie, the human rights lawyer. State-run news agency Xinhua called Mr. Xie's accusations of mistreatment "nothing but cleverly orchestrated lies" orchestrated by a legal team "aiming to cater to the tastes of Western institutions and media organizations and to use public opinion to pressure police and smear the Chinese government."

Mr. Xie's lawyer, Chen Jian'gang, has issued a detailed rebuttal of what he called "groundless lies" in those state media reports.

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In an interview Monday, Mr. Chen questioned why the 11-country letter was submitted quietly.

Had it been made public, "the effect would have been much stronger," he said. In a closed and restrictive system like China's, he said, "secret talk and private questions will have no effect whatsoever."

Joint diplomatic letters are rare, but becoming more common as countries seek a way to raise issues with China, while avoiding individual retribution from a government that often exacts revenge through economic means.

Last year, the U.S., Canada, Germany and Japan together expressed concern about three new Chinese laws on counterterrorism, cybersecurity and the management of foreign non-governmental organizations. Those laws, they wrote, had "the potential to impede commerce, stifle innovation, and infringe on China's obligation to protect human rights." The European Union submitted a similar letter.

Adding several signatures to one document was a way to raise attention in Beijing, said Guy Saint-Jacques, who was then Canada's ambassador to China.

"We came to the conclusion that the Chinese were not listening to what we had to say," he said.

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The letter "was badly received by the Chinese government. It accused us of ganging up on them," he said. It produced limited results. "There was an offer in one case to have more consultation, and there were some slight changes" to proposed legislation, said Mr. Saint-Jacques, who retired from the foreign service last fall. But "they didn't go as far as we would have liked them to go."

The new letter on torture, he said, comes at a time when "all observers agree that the human rights situation has deteriorated a lot under Xi Jinping," even as China has grown more confident in promoting the merits of its autocratic system to other countries.

The letter is notable, however, in part for who did not sign. Only seven members of the European Union participated; several diplomatic sources said unanimous support was blocked by Hungary, whose Prime Minister Viktor Orban has praised China's authoritarian model and sought Chinese investment. (The EU in January publicly called for an investigation into the handling of Chinese human rights lawyers, saying their alleged treatment, if verified "would amount to torture.")

The United States was also absent from the letter, which human rights workers took as a worrying sign of Washington's posture under Donald Trump.

"When a country like the U.S. is silent on this, it's really interpreted by Beijing as a free hand to do what they want. And that costs people their lives," said Sarah Cook, senior East Asia research analyst at Freedom House, a Washington-based watchdog on political, religious and economic liberties. "So it's unfortunate if the U.S. removes itself from that type of leadership role."

U.S. Secretary of State Rex Tillerson has pledged to keep pressing China on such issues.

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"I made clear that the United States will continue to advocate for universal values such as human rights and religious freedom," he said in Beijing on Saturday.

The latest U.S. report on Chinese human rights documents former prisoners and detainees who "were beaten, subjected to electric shock, forced to sit on stools for hours on end, hung by the wrists, raped, deprived of sleep, force-fed, and otherwise subjected to physical and psychological abuse."

The United Nations Committee against Torture, too, has criticized China for allowing torture to become "deeply entrenched" in its criminal justice system. In a late 2015 report, it urged Beijing to eliminate residential surveillance and hold criminally responsible any officials responsible for abuse.

Mr. Chen, the lawyer for Xie Yang, called residential surveillance a form of "illegal prison" that allows interrogators power to "do whatever they want."

But he held out little hope that real change is possible in authoritarian China, even if the residential surveillance is formally abolished. He pointed to previous Chinese practices of "re-education through labour" and "custody and repatriation" that were scrapped, only to have other abuse-prone forms of detention emerge.

"As long as there is poison in the system, you can remove one poisonous fruit today — and that looks good," Mr. Chen said. "But these kinds of poisonous fruit will grow out anew every day, without stop."