DETAILS of a mysterious UFO that shined bright rays of light onto a Soviet city in the 1970s have emerged from a treasure trove of declassified CIA documents published online.

Multiple reports from terrified locals described “very fine rays” raining down from the high-speed object, which appeared like a “huge star” over Petrozavodsk in what is now western Russia.

Dated September 1977, the once top secret CIA file appears to be a copy of a story published at the time by Russia’s TASS news agency.

It was released earlier this month as part of a dossier of newly uncovered declassified records on “Unidentified Aerial Phenomena” (UAPs).

Known as the “Black Vault”, the database is available thanks to a decades-long effort to access CIA records dating back as far as the 1970s.

According to one of hundreds of files in the vault, a peculiar UFO sighting above Petrozavodsk peaked the interest of agents almost 54 years ago.

“On 20 September, at about 0400 a huge star suddenly flared up in the night sky, impulsively sending shafts of light to the Earth” the report reads.

“The star moved slowly toward Petrozavodsk and spread out over it in the form of a medusa.”

The light then “hung there, showering the city with a multitude of very fine rays which created an image of pouring rain.”

After the rays ceased, the “medusa” turned into a bright semi-circle and moved in the direction of nearby Lake Onega.

A semi-circular pool of bright light, “red in the middle and white at the sides”, then formed in a shroud of grey cloud on the lake’s horizon.

According to citizen reports, the ordeal lasted between 10 and 12 minutes.

The CIA document states that what caused the phenomenon “remains a riddle”.

Russian weather experts reported having never seen anything like it, and no “technical experiments” were being carried out at the time.

“Many eyewitnesses” from various parts of the city reported sightings, meaning it was unlikely to be a mirage, the file says.

The document does not state whether the CIA followed up on the TASS report or simply filed it away for future reference.

It’s just one of a huge dump of CIA files uploaded to the free “Black Vault” database last week.