GENEVA >> China is systematically undermining international human rights groups in a bid to silence critics of its crackdown on such rights at home, a watchdog organization said Tuesday. The group also faulted the United Nations for failing to prevent the effort, and at times being complicit in it.

“China’s crackdown on human rights activists is the most severe since the Tiananmen Square democracy movement 25 years ago,” Kenneth Roth, the director of the agency, Human Rights Watch, said in Geneva today at the introduction of a report that he described as an international “wake-up call.” “What’s less appreciated is the lengths to which China goes to prevent criticism of that record of oppression by people outside China, particularly those at the United Nations.”

“The stakes are not simply human rights for the one-sixth of the world’s population who live in China,” Roth added, “but also the survival and effectiveness of the U.N. human rights system for everyone around the globe.”

The report highlights China’s measures to prevent activists from leaving the country to attend meetings at the United Nations, its harassment of those who do manage to attend and the risk of reprisals when they return or if they interact with U.N. investigators inside or outside China.

The report also noted barriers placed by Chinese officials to visits by U.N. human rights officials. Beijing has not allowed a visit by the agency’s high commissioner for human rights since 2005, and continues to delay 15 requests for visits by special rapporteurs working on political and civil rights issues.

China allowed visits by four rapporteurs since 2005 on issues like poverty, debt and the status of women. But it carefully choreographed those visits, and contacts not sanctioned by the state posed risks to those involved. The United Nations has expressed concern that the detention of Jiang Tianyong, a prominent human rights lawyer, resulted from a 2016 meeting in Beijing with the U.N. special rapporteur on poverty, Philip Alston. Jiang disappeared for several months and was later charged with subversion.

The report also documents China’s diplomacy in the U.N. Human Rights Council in Geneva, where the country aligns with an informal collection of states, including Algeria, Cuba, Egypt and Venezuela, that discretely coordinate their positions to deflect scrutiny of their records and consistently challenge the council’s ability to look into accusations of abuse in other states without their consent.

“It’s becoming a mutual defense society among dictators in which everybody understands the need to deflect criticism of you today because they may criticize us tomorrow,” Roth said. “And China is an active, willing partner in that effort.”

Moreover, China has withheld information requested by U.N. bodies that monitor issues like torture, treatment of the disabled and children’s rights, and has tried to stop the filming and online posting of their proceedings, Human Rights Watch said. The report also accused China of using its position on a U.N. committee that accredits nongovernment organizations to obstruct applications by civil society groups.

Individual measures by China could be passed over as unremarkable, Roth said, “but when you put it all together, what it represents is a frontal assault on the U.N. human rights system.”

Human Rights Watch delivered a copy of its report to China but received no substantive response, he said.

A spokesman for China’s foreign ministry, Geng Shuang, told reporters in Beijing that China played an active role in the United Nations’ human rights work. He called the report’s accusations “groundless.”

“We urge the relevant organization to remove their tinted lenses and objectively and justly view China’s human rights development,” Geng said.

The effect of China’s behavior on human rights is like “death by a thousand cuts,” Roth said, but he also pointed to the dangers of “a thousand acts of acquiescence” by the U.N. and states that support human rights.

Human Rights Watch presented a copy of its report to U.N. Secretary-General Antonio Guterres, Roth said, but Guterres’ response did not mention China by name.

“That illustrates what needs to change,” Roth said. A request for comment from Guterres’ office was not immediately returned.

The report cited the United Nations’ treatment of Uighur rights activist Dolkun Isa, who had received U.N. accreditation to attend meetings in its New York headquarters but was escorted off the premises by security officers without explanation.

It also cited the exceptional treatment that the U.N. accorded President Xi Jinping of China when he visited its Geneva headquarters in January: It sent home many staff members early, refused access to nongovernment organizations and granted access to only a handful of journalists.

Its handling of the occasion “was an utter embarrassment for the U.N.,” Roth said. “It became actively complicit in Xi Jinping’s terror of any criticism. It was an utter abandonment of the principles the U.N. should abide by. It was a shameful moment.”