There are also included three pictures of the alleged extraterrestrials. One of the photos - taken by British student Alex Birch in 1962 - claimed to show a group of flying saucers flying over the city of Sheffield in the UK. However, the photo was proven to be a hoax.
The files also detail a case of flying saucers that were spotted over what was formerly Belgian Congo. The document reveals that two "fiery discs" were seen over a uranium mine and that the discs had "glided curves and changed position many times."
"Suddenly, both discs hovered in one spot and then took off in a unique zigzag flight to the north east. A penetrating hissing and buzzing sound was audible to onlooker below. The whole performance lasted 10 to 12 minutes."
Also contained in the files is the case in Socorro, New Mexico, in 1964, when police officer Lonnie Zamoraspotted a large flame rise from the ground and pierce the sky above a remote patch of desert. He went to investigate and found a shiny object the size of a sedan perched on the hilltop, which was oval in shape and aluminum in color. The object then began to rise into the air and then sped away from him over the mountains and disappeared.
The CIA has always denied having any proper intelligence about aliens. But it has often organized scientific panels to discuss the nature of these allegedly alien objects.
The release of the documents coincide with the long-awaited return of The X-Files on Sunday. The beloved show was rebooted by the Fox Network after 10 years, with its two original stars reprising their roles.
Stephen Bassett, executive director of the Paradigm Research Group, who is campaigning for the US government to admit aliens are visiting Earth, told The Mirror that the CIA appears to have used the return of The X-Files to their benefit.
"It appears the CIA used the revival of the X-Files franchise as a convenient time to remind the public the agency has, in fact, engaged the extraterrestrial presence issue in the past. Post-disclosure the CIA will have substantial public relations issues as it has played a significant role in maintaining the truth embargo over six decades. These recent postings could have an inoculative effect in service to the agency's future PR strategy."