A trove of previously top secret National Security Agency records have just been released that detail a spate of apparent UFO encounters, including one incident where 13 military fighter jets were sent to chase a mysterious unidentified object.

The UFO-related files, made public by the nonprofit Disclosure Foundation earlier this week, are all marked with the codeword “Umbra” — a top security designation used by the NSA.

The documents, which are separate from the wave of newly declassified UFO files released by the Pentagon, detail unexplained sightings from witnesses, as well as radar-tracking reports and incidents involving military aircraft.

One heavily redacted intelligence report details how more than a dozen military jets once tried to chase down an object spotted in the sky.

In other incidents, Soviet-made fighter jets described pursuing unknown objects.

Radar-tracking reports included in the files also described UFO objects as being star-shaped, spheres and “balls of fire.”

“The object was going up and down at a fast speed and a very high altitude,” one report noted of an alleged UFO sighting, adding that it had a “white luminous light.”

The documents, which were released as part of a Freedom of Information Act appeal from the Disclosure Foundation, are tied to a 1980 lawsuit brought against the NSA that sought to compel the release of UFO-related information in the agency’s possession.

As part of the suit, NSA’s chief policy officer Eugene Yeates submitted affidavits in response to a document request, which later became known as the “Yeates Memo.”

The memo was declassified and made publicly available back in 2009 but the information included in the document wasn’t released.

“When our legal team requested the underlying supporting material that was used to produce Mr Yeates’ classified memo to the court, the NSA denied the request in its entirety. We challenged that denial, and after a lengthy appeal, the NSA appeals authority acknowledged that its blanket denial was improper,” the Disclosure Foundation said.

“We are pleased to report the production of hundreds of pages of documents spanning many prior decades, nearly all of which were previously classified as ‘TOP SECRET UMBRA’.”

The release came just days before the Pentagon released its latest batch of declassified UFO files on Friday, including audio of the Apollo 12 crew describing how they once saw mysterious “streaks of light” while trying to sleep in deep space.

The 222 files released were among the second batch of documents made public on the Department of War’s website – weeks after President Trump ordered the release of government reports on unidentified flying objects.