The Central Intelligence Agency has admitted that it was responsible for at least half of reported UFO sightings in the middle of the last century due to its secret, high-altitude reconnaissance flights.

The 1950s and '60s was an intense period when a number of Americans reported UFO sightings and alien visitations. These sensational events lent cinematic credence to a number of Hollywood space blockbusters, including Steven Spielberg’s "Close Encounters of the Third Kind" and "ET," and George Lucas’s "Star Wars."



Now it appears the unidentified flying objects were more fact than fantasy, while the mind behind them was not quite alien.



This week, the CIA took to social media to claim responsibility for at least half of UFO sightings in the 1950s and 60s.



"Reports of unusual activity in the skies in the '50s? It was us," the agency tweeted, while acknowledging the section on UFOs attracted the most attention to its website in 2014.

#1 most read on our #Bestof2014 list: Reports of unusual activity in the skies in the '50s? It was us. http://t.co/BKr81M5OUN (PDF 9.26MB) — CIA (@CIA) December 29, 2014

The CIA tweet linked to a heavily redacted 272-page document, entitled ‘The CIA and the U-2 Program, 1954-1974’ that described reconnaissance missions at altitudes in excess of 60,000 feet that sparked speculation on the ground.



“High altitude testing of the U-2 soon led to an unexpected side effect – a tremendous increase in reports of unidentified flying objects (UFOs),” the 1998 report noted.



The CIA said that many of the people who reported UFO sightings around this time were commercial pilots, who caught occasional glimpses of the high-altitude aircraft while flying at considerably lower altitudes.



The silver wings of the U-2 spy planes “would catch and reflect the rays of the sun and appear to the airliner pilot, 40,000 feet below, to be fiery objects,” it revealed.



“At this time, no one believed manned flight was possible above 60,000 feet, so no one expected to see an object so high in the sky.”



In general, the CIA document admitted to being responsible for “more than half” of the UFO sightings, many are left wondering what or who was responsible for the other half of reported sightings.



The agency’s previously unclassified document said the CIA could not explain to people who believed they had really witnessed UFOs a true cause of some of those sightings.

To the Soviet Union, however, the U-2 spy plane was not so “unidentified.”



On May 1, 1960, an American U-2C spy plane, piloted by Gary Powers, was shot down in Russia's Urals region by surface-to-air missiles. The sensational incident was to be a major embarrassment for US President Dwight D. Eisenhower, who was forced to admit that the US had engaged in secret espionage activities.

READ MORE:CIA declassifies Area 51, no mention of UFOs, extraterrestrials

Powers parachuted safely from the aircraft and was convicted of espionage against the Soviet Union, but was released in a prisoner swap with US officials in February 1962.



Today, the wreckage of the U-2 aircraft, as well as items from Powers' survival pack, are on display at the Central Armed Forces Museum in Moscow.