MOSCOW: A new film by a Hollywood director has revived a mystery of how a group of Soviet hikers met their grisly deaths on a Russian mountainside in unexplained circumstances more than 50 years ago.

The film, "The Dyatlov Pass Incident", loosely retells the true story from 1959 when nine students went on an expedition to a peak in the northern Urals known as the Mountain of the Dead - never to return.

Soviet investigators found the students' bodies scattered over a large area, while their tent had been cut open from the inside.

One man's body registered a high level of radiation, while one woman's tongue had been cut out. Some of the bodies were strangely discoloured or had missing eyeballs. Others had fatal internal injuries but no outer signs of trauma. Many seemed to be frozen in attitudes of horror.

Few believe that the hikers' death was an accident - and conspiracy theories abound as to exactly what happened on the mountain.

The English-language film by action and horror director Renny Harlin, best known for "Die Hard 2" and "A Nightmare on Elm Street 4", updates the story with a group of five naive American students visiting the scene and travelling through time to encounter the original group

The film has American, British and Russian actors, both US and Russian producers and was filmed partly on location in Russia's Far North Murmansk region, but it puts a distinctly Hollywood spin on the story.

In one scene, a tear-stained blonde woman stares into a wobbly camera in grainy green footage reminiscent of 1999 horror smash hit "The Blair Witch Project."

"Jason, we're not going to get out of here!" she wails.

In Harlin's film the students travel back in time and see Soviet soldiers hiding the bodies in a top-secret bunker used for experiments.

To up the conspiracy levels, the director references the so-called Philadelphia Experiment, in which the US navy allegedly tested teleportation in 1943 - and throws in some hungry zombies for extra gore.

--Secret of the fireballs --

The real-life case was investigated by the military who came to the mysterious conclusion that the group had died from "a natural force they were unable to overcome." They closed the file and classified it as secret.

Suppressed during the Soviet era, the incident was brought back into the public eye in the 1990s when the investigator who worked on the case, Lev Ivanov, wrote an article about it called the "Secret of the fireballs," which suggested that the students were killed by some kind of energy from strange fireballs seen in the sky at the time.

His account sparked a host of outlandish theories in books and documentaries and on the internet -- including that the group were attacked by native people for trespassing onto a sacred site, or that the culprits were yetis or aliens.

Others suggest that they could have witnessed testing of some kind of non-standard weapon, or that the military simply killed them because they saw something they shouldn't have.

The one survivor, Yury Yudin -- who left the expedition early -- told Komsomolskaya Pravda newspaper last October that he believed the group accidentally witnessed secret tests and became contaminated.

"If they were really killed by a natural force, then there would be no secret, and we would not be talking about this 53 years on," he said.

--- 'It's our own version' ---

Harlin's film does not claim to uncover the truth behind the incident.

"It's a strange, mysterious story, it's our own version," one of the Russian producers, Sergei Melkumov, told AFP.

"It's not a Russian version or an American version. It's a made-up story, shot by an American director."

Melkumov said his film company Non-Stop Production received 60 million rubles ($1.95 million) for the production from the government Cinema Fund, which subsidises a number of major film companies.

The film has largely been perceived as American in Russia, however.

It was released in Russia on February 28 and agreements have been signed to release it in Eastern Europe, Melkumov said, but no US release has yet been agreed.

The film, which had a budget of $4.5 million, has so far made $4.2 million at the box office, according to Variety Russia.