Hundreds of newly released documents give insight into Cold War-era UFO sightings tracked by military radar systems worldwide

An incident involving 13 Soviet-designed MiG fighter jets chasing a mysterious star-shaped UFO was among the encounters described in newly declassified top-secret files released after a decades-long legal battle with the US intelligence community.

The Disclosure Foundation, a US nonprofit advocating greater transparency on UFOs, said on Sunday it had secured 334 pages of records from the National Security Agency, the country's eavesdropping service, after winning a Freedom of Information Act appeal. The heavily redacted files - many marked "TOP SECRET UMBRA," one of the US intelligence agency's highest classifications - contain Cold War-era radar reports and intelligence messages on unexplained objects tracked by military systems worldwide.

One of the most dramatic incidents described 13 MiG fighter jets being scrambled after military radar detected a single unidentified object.

The NSA files do not specify where or when the incidents occurred or identify witnesses. However, repeated references to Soviet-made MiG fighter jets suggest some encounters unfolded during the Soviet period, including one report over China and another describing six MiGs "attacking said UFO."

Other files describe encounters with star-shaped, disc-like, spherical, and cigar-shaped craft. One report detailed an "elongated ball of fire" that split into three glowing objects while moving across the sky.

In one witness account, an object emitted a "white luminous light" with a slightly "bluish" color. The report said it moved rapidly in vertical motions at high altitude and "kept turning around." Another file described a "spherical or disc-like" UFO that was "brighter than the sun and about half the Moon's diameter."

The documents were released after the NSA initially denied access requests, extending a legal battle over UFO-related records dating back to a 1980 Freedom of Information Act lawsuit against the agency.

The release follows the Trump administration's publication of more than 160 UFO-related files earlier this month. The disclosure push came after earlier declassification orders tied to the assassinations of John F. Kennedy, Robert F. Kennedy, and Martin Luther King Jr., and amid renewed debate sparked by former President Barack Obama dismissing claims the US was concealing evidence of alien contact.