'It is only a matter of time' before an aircraft crashes into a UFO on Earth, a top politician has warned.

The world needs to step up its probe into 143 unexplained close encounters between unidentified aerial phenomena - or UAP - and military jets before tragedy strikes, according to US Congressman Tim Burchett.

Though defence chiefs and US space agency NASA have launched separate probes into potential alien craft the 57-year-old politician has warned progress has not been quick enough.

He has called on the US Government to make public all the records it holds on UFO sightings and Top Gun pilots who claim to have had close encounters to be called to give evidence to Congress.

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