The announcement came 60 years after nine experienced hikers led by Igor Dyatlov perished on a remote Urals hillside on the night of February 1, leaving relatives still wondering about their cause of death and sparking a host of conspiracy theories.

"Relatives, the media and the public still ask prosecutors to determine the truth and don't hide their suspicions that something was hidden from them," the Prosecutor-General's spokesman Alexander Kurennoi said on an official online video site.

Searchers first found the nine hikers' tent abandoned and cut open, and then their bodies scattered over the mountainside with terrible injuries, after a week of an aerial search of the area.

The hikers became known as the "Dyatlov group" and their mysterious end as the "Dyatlov Pass Incident".

A criminal case was opened on February 26 and closed thee months later. It remained classified until the 1970s.

The probe was closed after Soviet investigators concluded their deaths were not murder without providing a different cause of death. Unanswered questions and rumours have tickled the public's imagination for decades.

On Friday, Russia's TV-3 channel aired a trailer for its upcoming "Dyatlov Pass" mini-series, which suggests a paranormal explanation for what happened.

Among the different theories circulated over the decades were an attack by escaped convicts, indigenous people or a yeti-like creature. There was also talk of an explosion caused by a secret weapons test, falling rocket debris, or even some unknown psychological force that drove the hikers to leave their tent in the night and kill each other.

Prosecutors have combed through 75 different theories, said Andrei Kuryanov, the prosecutor who has been charged with the comprehensive review of the Dyatlov Pass case since September.

"We threw out some of the theories right away," he said. "The phantasmagoric ones included flying saucers, or anything otherworldly."

The possibility of murder was also discarded, he said, though the new review will include a fresh medical examination of the remains.

Kuryanov said injuries were found to have been inflicted post-mortem and the victims' extensive head trauma was caused by the freezing of the corpses.

He added the incident was likely from "natural" causes.

A group of experts will travel to Dyatlov Pass later this year to take samples, after which weather experts will rule whether the deaths could have been caused by an avalanche.