Torture perpetrated by Russian officers against Ukrainian civilians and prisoners of war has reached such a level that it is clearly a systematic, state-endorsed policy, a United Nations expert on torture said Saturday.

Witnesses shared accounts that were credible, said Alice Jill Edwards, the U.N. Special Rapporteur on torture, and that confirmed a consistent pattern of torture, including rape and beatings, in different detention facilities under Russian occupation and among Ukrainian soldiers captured by Russian forces. She spoke in an interview on Saturday as she wrapped up a seven-day visit to Ukraine.

“This is not random, aberrant behavior,” Ms. Edwards said. “This is orchestrated as part of state policy to intimidate, instill fear or punish to extract information and confessions.”

Her comments were one of the strongest condemnations implicating the Russian leadership by an independent expert since Russia’s full-scale invasion last year. She said she had reached out to Russian authorities at least seven times since receiving her mandate a year ago, drawing attention to the behavior of its troops and personnel in its detention facilities, but had received no response. Moscow has denied it practices torture, she said, but its refusal to address the issue, and the accumulating cases, amounted to tacit approval of its use.

“Russian authorities have failed so far to send a directive to their soldiers and the military command informing them that torture and such types of detentions and interrogations are not acceptable,” she said. “They deny they do it, but show me the military directive where torture is prohibited.”

Moscow had failed to respond even to her recent offer to visit and report on the conditions of Russian prisoners of war held in Ukraine, she added. An Australian lawyer and academic, Ms. Edwards said she had twice been obliged to postpone visits to Ukraine for security reasons, but the buildup of evidence had made a visit in person imperative.

Last week she made public details of four individuals who had told her they were tortured while detained under Russian occupation in the region of Izium in northeastern Ukraine last year. Ukraine has opened 103,000 general cases for prosecution related to the conflict, she said.

Of hundreds of Ukrainian prisoners of war held by Russia and released in exchanges, Ukrainian officials have said 90 percent suffered torture, including sexual violence, she said.

“The scale is neither random nor incidental,” she said.

Former prisoners of war held by Russia suffered a dangerous level of weight loss from starvation during their detention, she said. One former prisoner told her he had lost 40 kilograms — almost 90 pounds — during incarceration, and his hair had turned gray. Some described fellow prisoners dying in custody from beatings or poor conditions.

She also met a woman who described suffering two heart attacks while in detention after enduring torture and being forced to watch her son being tortured. “This was so distressing to her that she was ready to sign any document that there was,” Ms. Edwards recounted. Even after signing a confession, the woman was held for an additional 300 days, she added.

“There is a structure to it,” she concluded. “Someone is supervising it, someone is perpetrating it, and someone is interrogating and has this role to do that.”

Ms. Edwards is well known for her work on sexual violence, in particular during the conflict in Bosnia and Herzegovina, and for her breakthrough legal argument, now accepted globally, that rape and sexual violence are forms of torture and persecution.

Yet she expressed frustration that during her visit she was not able to advance far with cases of sexual violence against women in the Ukrainian conflict. Relatively few Ukrainian women have come forward to prosecutors with complaints of sexual torture or crimes, she said. Especially in rural areas, women suffer from the stigma of sexual abuse and are deterred by the added threat of accusation of collaboration. At least one rape victim has been charged with collaboration, she said.

Men, who also suffered sexual torture in detention, have come forward in larger numbers, she said. There is evidence that it is a larger problem for women. One nonprofit organization found increased demand for the morning-after pill from women in areas that were recaptured from Russian forces, she said.

Ms. Edwards said that the coercive environment of the conflict zone was enough to establish lack of consent in cases of sexual violence. But she added that Ukraine needed more female investigators and more training in investigation and interviewing techniques to establish rapport and allow women to open up.

“Women and men need to feel safe that this is something they can speak about,” she said, “and of course necessarily get all the treatment they need and get the help to be able to recover from it.”