The Central Intelligence Agency (CIA) has recently taken responsibility for at least half of all UFO sightings between 1950s-60s, it has been reported.
A previously confidential CIA document has revealed that most of the sightings were actually U-2 spy planes, News.com.au reported.
The report, 'The CIA and the U-2 Program, 1954-1974', written by Gregory Pedlow and Donald Welzenbach, outlines the CIA's involvement in the development of the U-2 spy plane. It explains how the testing of the planes led to a massive increase in UFO reports.
The sensational 272-page document reveals how the agency tested U-2 spy planes at altitudes of 60,000ft above countries such as the Soviet Union.
At that time, most people were not aware manned flights were possible at these heights so many, including several pilots, reported sightings as UFOs.
In the mid-1950s, most commercial airliners flew between 10,000 and 20,000 feet, while military aircraft such as B-47s and B57s flew below 40,000 feet.
The document goes on to reveal that the CIA cross-referenced UFO sightings to U-2 flight logs and this enabled the investigators to eliminate the majority of the UFO reports although they could not reveal to the letter writers the true cause of the UFO sightings.