Tatiana Shorokhova, a film critic from St Petersburg, has admitted to feeling sick and “physically afraid” while watching DAU. Natasha, a controversial film by Ilya Khrzhanovsky produced from a years-long experiment on an immersive set built as a replica of a Soviet-era research institute. In fact, she likened the experience to rape.

It was not just the graphic scenes of violence against the titular character or depictions of real sex while drunk, she said, but the understanding that all of this was, in a way, real.

The largely unscripted shoot involved thousands of people – most of whom were not professional actors – eating, sleeping and living as though they were in the Soviet Union (some have nicknamed the film the Stalinist Truman Show).

Actors wore Soviet-style clothing and were banned from using mobile phones on set. One, a real-life prison warden who played a brutal official in the film, described the experience as a “kind of metamorphosis”, a “parallel world” similar to “hypnosis”. However, he denied being sucked in.

The film-makers’ main response to criticism has been that all the actors were there of their own free will and could stop the action any time they wanted to. Some reviewers have hailed the DAU. Natasha as an achievement in replicating the terror of life under authoritarianism.

And then Shorokhova and four other Russian film critics at the Berlin international film festival wrote an open letter to the festival’s leadership that raised ethical questions over its selection of the film.

A still from DAU. Natasha. Critics who complained about the film say they were accused of being prudish. Photograph: Phenomen Film

Their questions were simple. First, in the immediate aftermath of the Harvey Weinstein scandal, why is it acceptable to select a film that contains scenes of real psychological and physical violence against non-professional actors? Second, could DAU. Natasha have ever been made in a western country with western actors? And third, was the film’s consideration for a prize encouraging mistreatment of talent in the name of art?

The backlash was immediate, Shorokhova said. She described a torrent of criticism on social media that ranged from considered feedback to violent threats. “Me and my friends wrote just three questions to the Berlin film festival and we became a pariah basically,” she said.

Broadly, they have been accused of writing a Soviet document, a donos, or denunciation, of the film, which went on to win the best cinematography award at the festival.

Shorokhova said she did not regret writing the letter, citing the support they had received from “good people”, because she hoped the issue would be raised at subsequent festivals where products of the Dau experiment may be screened.

“It’s an important thing that we have started asking questions of film festivals. Because [they] are all speaking about gender parity, about the women in competition, and really? You have this ugly film depicting the torture of a woman? What for?”

In one reportedly simulated scene that has gained notoriety, Natasha is forced by a Soviet security officer to insert a cognac bottle into her vagina.

Shorokhova said she had been accused of being prudish about the film, the brainchild of the Russian director Ilya Khrzhanovsky, which was closely guarded through the editing process. Only now is she seeing some of its 700 hours of film.

Actor Jeremy Irons (right) presents Jürgen Jürges with an award for DAU. Natasha at the Berlin film festival. Photograph: Andreas Rentz/Getty Images

“Everyone is saying I am against violence and sex on screen. No, I love a good sex scene. But it should not be unethical when you shoot it,” she said.

In various interviews, including one published in the Guardian in January, Khrzhanovsky and the other film-makers have denied that abuse took place.

Carlo Chatrian, the artistic director of the Berlin film festival, said “concrete allegations” should be addressed to the production company, and that the actors in the film had denied abuse during a press conference.

Natalia Berezhnaya, who plays Natasha, said told reporters before the film was screened that the actors were “in charge of our own senses and emotions. We were well aware of what we were doing.”

The cinematographer Jürgen Jürges agreed. “In those scenes we always had a safety vow. If somebody did not want to go along, we could stop at any time,” he said.

Visitors to the closed set in Ukraine described a promiscuous, alcohol-soaked environment where Khrzhanovsky was revered. Some embraced the experience; others recoiled from it.

In 2011, one actor recalled to Michael Idov, a writer and film-maker, how the director questioned her on her sex life, including when she lost her virginity and whether she would be willing to sleep with other women. (Khrzhanovsky later told the Guardian that he did discuss sex with actors, though not crew members, and denied he ever abused his position.)

We are greater than individuals and their concerns. Albina Kovalyova, casting director

Last year, the French newspaper Le Monde also published allegations that some real neo-Nazi extras on set (including one serving time in prison for assault) had repeatedly physically attacked an American artist. Idov said he regretted “not focusing on the victims’ stories more in 2011”.

It has been difficult to balance the project’s outsized ambition with the ethical questions it has raised. Albina Kovalyova, who worked as a casting assistant and later documented the project, wrote last year that the film was a “powerful work of art” but also suggested Khrzhanovsky’s experiment may have “crossed the line from fictional abuse to the real thing”.

She felt “cruelly manipulated” by a scene that depicted experiments being performed on babies with Down’s syndrome, even after Khrzhanovsky insisted they had not been ill-treated.

In an interview, Kovalyova described the philosophy of the film’s creators: “We are greater than individuals and their concerns. It’s about the big game.”