The United States is probing 510 UFO sightings.
The US are investigating more than 500 UFO sightings
A declassified intelligence report has revealed that most of the crafts posed a threat to national security as they were in military airspace close to nuclear weapon sites and power plants.
Officials say that they found no evidence of alien life but the US government still regard the unidentified objects as a threat.
The Pentagon confirmed last year that it was investigating 144 sightings of mystery craft dating back to 2004 but now says the number of reports under investigation had nearly quadrupled.
In its 2022 report, the Office of the Director of National Intelligence said that the events "continue to occur in restricted or sensitive airspace, highlighting possible concerns for safety of flight or adversary collection activity".
The report claims that efforts to destigmatise the reporting of UFO sightings was likely to have contributed to the increase in numbers.