The new documentary “Under the Sun” follows an 8-year-old North Korean girl named Zin-mi as she prepares to join the Korean Children’s Union, run by the Workers’ Party. Zin-mi and her parents — her mother works in a soy-milk plant, her father is an engineer at a garment factory — share abundant family meals, ride Pyongyang’s spotless subways and pay their respects at a bronze statue of North Korea’s founder, Kim Il-sung.

There’s just one problem: The action is fake. The North Korean government cast the film, wrote the script and provided guides to feed the actors their lines while managing every detail of the project. In reality, Zin-mi’s father is a journalist, and her mother a cafeteria worker. “Don’t act like you’re acting in a movie,” a guide scolds the girl at one point. “Act naturally, like you do at home.”

So, why did the director Vitaly Mansky, a documentary maker in the cinéma vérité tradition of Frederick Wiseman and D. A. Pennebaker, agree to such an awkward, not to mention morally dubious, arrangement? “My dream of visiting North Korea,” he said, “was the desire to understand something about the past of my country, my family.”

Mr. Mansky, who was born and raised in the Soviet Union, divides his life into two periods: before and after 1991, when the government collapsed and he set out at 28 to document the way people had lived under Communism. “A documentary provides the possibility of riding in a time machine,” he said by Skype from his home in Riga, Latvia. For “Motherland or Death” (2011), he traveled to Socialist Cuba, which he likened to the ’70s-era Soviet Union. “Under the Sun,” which opens theatrically July 6, uses contemporary North Korea as a proxy for Stalin’s Soviet Union.

In 2012, Mr. Mansky met a North Korean delegation at a Vladivostok film festival and spent the next two years negotiating with the government for access. Under the final contract, in addition to providing the script, the actors and the guides, North Korea censors would vet daily footage and retain final approval over the finished film. Mr. Mansky would not be allowed to talk to the actors or film anything other than sanctioned scenes.

Mr. Mansky, though, persevered in the face of such absurdity. “I saw my illusions dissolve into thin air,” he said. “But even then I believed I could make the film I wanted to. I’ve had lot of experience working in confined spaces, whether it is filming the army, in a prison or inside the Kremlin. One way or the other, I’ve always managed to reveal the true essence of the situation.”

He took as his model Leni Riefenstahl’s “Triumph of the Will,” her film about the 1934 Nazi Party Congress, which is considered both a masterpiece of propaganda and an important documentary. “I thought this would satisfy the North Korean regime on the one hand,” he said, “and give the world a view of the real North Korea on the other.”

Extreme limitations called for extreme measures, so Mr. Mansky employed the techniques of undercover journalism. Unknown to the North Koreans, he left his cameras running all day, documenting each scene being set up, rehearsed and reshot. We watch a North Korean guide put workers through several takes at the milk plant until they display the proper level of enthusiasm.

“Comrades, today our workshop beat the government quota with 150 percent!” a seamstress announces at the garment factory. By the next take, production has risen to “200 percent over quota.” When Zin-mi is asked how she feels about joining the Children’s Union, she is clearly overwhelmed by her new responsibilities, and two fat tears roll down her face. “Stop her crying,” a guide says off camera.

How did Mr. Mansky get these scenes through the censors’ daily edit? His cameras held two memory cards, and at the end of each day, one crew member would create a delay so that another had time to copy it. Mr. Mansky then handed the card to the censors, who overnight removed anything they found objectionable.

Such close state scrutiny reminded Mr. Mansky a bit too much of life in the Soviet Union. He grew paranoid, he said, and every night blocked the doors of his hotel room with furniture to prevent someone from stealing the footage while he slept. Crew members suspected their rooms were bugged and discussed the project in code, he said. As a final precaution, Mr. Mansky hired a Russian expert in Korean and trained her to run the sound equipment. “She was our spy,” he said. “It helped us know what they were planning for us.”

Mr. Mansky’s inventiveness was inspired by the methods used by Dziga Vertov, an early-20th-century Russian documentary maker, in “Man With a Movie Camera” (1929).

“Vertov had a whole bunch of techniques for capturing ‘life unawares,’ like hiding cameras, surprising people by sticking a camera in their face, distracting people with a fake camera and generally catching them off guard,” said Jeremy Hicks, a scholar of Russian film at Queen Mary University of London. Mr. Hicks called “Under the Sun” Mr. Mansky’s “most Vertov-like film” because of the lengths it goes to show the audience how it was made. For instance, text hovers over shots to reveal the truth behind the carefully curated illusion. “The script of this film was assigned to us by the North Korean side,” reads one.

The formal principles that guide Mr. Mansky can be found in a manifesto he published in 2005. North Korea might have done well to read its first line: “Script and reality are incompatible.” The contract between North Korea and Mr. Mansky broke down in 2014, as he prepared for his third trip to North Korea. The visas didn’t arrive, and Mr. Mansky couldn’t reach his North Korean partners. With no more access, Mansky was left to edit hundreds of hours of footage into a finished film.

He didn’t hear anything from North Korea until “Under the Sun” began receiving praise at film festivals. The government’s Ministry of Culture contacted its Russian counterpart (which had financed some of the film), demanding it destroy the film and punish the filmmaker, which Russia didn’t do. Moscow, though, did ask Mr. Mansky to remove its name from the credits, but he refused. In an article, a former culture minister, Mikhail Shvydkoy, accused Mr. Mansky of endangering the lives of the North Koreans who participated in his documentary.

Mr. Mansky argues that his moral dilemma was whether to make the documentary in the first place. Further, he said, he took precautions to protect Zin-mi and her family. “I was very worried about them, which is why I didn’t include some footage that would have harmed them.” In May, the North Korean news media reported that Zin-mi presented flowers to Kim Jong-un, the country’s leader, at the Party Congress.

(In January, a Museum of Modern Art curator, worried about retribution from North Korea, removed “Under the Sun” from its Doc Fortnight festival. According to emails provided to The Times by the film’s German producer, the curator cited the Sony Pictures hack in 2014, when a group thought to be associated with North Korea leaked company emails and demanded that Sony not release “The Interview,” a satire of the country. In June, Rajendra Roy, the museum’s chief film curator, said the film was “wrongly disinvited.”)

After “Under the Sun” won the best director award at the Tallinn Black Nights Film Festival in Estonia, the North Koreans invited Mr. Mansky back to discuss an “urgent issue.” “I’m not stupid,” he said. “I knew what would happen if I returned.”