The Department of Defense has released a further batch of previously classified files on alleged UFO sightings to provide what it called 'unprecedented transparency' to the American people.

Experts said the batch of around 160 files released on Friday contain new videos of known "unidentified anomalous phenomena" sightings but give no conclusive evidence of alien technology or extraterrestrial life.

"The materials archived here are unresolved cases, meaning the government is unable to make a definitive determination on the nature of the observed phenomena", they added in a statement attached to the tranche of files.

Donald Trump is the latest president to release US government reports on UFOs, a disclosure process that began in the late 1970s.

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