PARIS — The French Culture Ministry ruled Wednesday that a new documentary film on Islamic radicals was unsuitable for minors, saying that it offered images of violence that were “sometimes unbearable” and interviews with members of Al Qaeda and other extremist figures that provided a platform for propaganda.

The documentary, “Salafistes,” will also be accompanied by a warning about its contents. It shows one leader of the Salafists, who practice a fundamentalist form of Islam, supporting the Sept. 11 attacks in the United States and another leader justifying the amputation of hands as a punishment under Shariah, the legal code of Islam. They also speak freely about their opinions on the inferiority of women.

The decision to restrict a movie to those 18 and over is usually reserved for films with pornographic content or extremely violent scenes, and is very rare for documentaries in France, which has been grappling with how to balance freedom of speech and expression with national security after a series of deadly attacks last year. This month, the distributors of “Made in France,” a film about fictional homegrown jihadists, decided to cancel its release in theaters, citing security concerns.

The documentary starts with a tour of Timbuktu, Mali, under the occupation of jihadists in 2012 and ends with propaganda images of the Islamic State last year. The images inspired the movie “Timbuktu,” directed by Abderrahmane Sissako, which was nominated for an Oscar for Best Foreign Language Film.

“We wanted to show what it was like to live under the Shariah when we started the project, but then Daesh emerged and we had to put it in the synopsis,” said François Margolin, who directed the French film with Lemine Ould M. Salem, a journalist from Mauritania, using another term for the Islamic State.

“Salafistes” was among the films to be shown at the FIPA festival in Biarritz in southwestern France. Just before the first screening the National Center of Cinematography, which assigns movie ratings, called the festival to say that the documentary was “degrading human dignity” because it showed images of a police officer killed in the attacks of the satirical newspaper Charlie Hebdo last year.

In response, the festival restricted the screening only to those with credentials, like reviewers and journalists.

The cinematography center recommended that the film receive an under-18 restriction and a warning message. Mr. Margolin and Mr. Ould Salem cut that scene and submitted the new version Tuesday.

But after watching the second version, the culture minister, Fleur Pellerin, who has oversight on ratings, agreed with the center, which argued that the film did not provide any counterpoint to the extremists, some of whom called for the murders of Jews and Christians.

Mr. Margolin said he had not expected the film to be rated at all. “The interviews explain the ideology of these people, and the propaganda images are here to show in practice how their ideas work,” he said Tuesday. “People are intelligent enough to understand the contrast.”

At the film’s Paris premiere on Tuesday night, the audience was split, with some arguing that the movie had the courage to “look evil in the eye,” while others thought it amounted only to propaganda.

The rating is also proving to be a financial blow to the directors. “Salafistes” had been scheduled to open in 30 theaters nationwide but will instead open in just three.

“We are going to lose a lot of money despite the fact that we risked our lives to shoot some scenes,” Mr. Margolin said.