A former top US defense official believes UFOs pose a “vital national security issue” — and says America isn’t the only country that’s been grappling with unexplained sightings.

Christopher Mellon, a former deputy assistant secretary of defense for intelligence, said US Navy pilots who recently reported seeing UFOs on a near-daily basis in 2014 and 2015 have legitimate concerns.

“They’re deeply frustrated and that is the core of our show,” Mellon said in an interview with “Fox & Friends” Wednesday, where he pushed his forthcoming History Channel series “Unidentified” about the phenomenon.

“The pilots’ concerns are, one, there have been near-midair collisions, so there is a safety issue,” Mellon continued. “Two, there is a vital national security issue which is that our sovereignty is being violated by vehicles of unknown origin.”

He hinted that the US isn’t alone in its sightings of possible alien life.

“We’re going to be presenting information from a NATO ally that’s been having very similar experiences,” said Mellon.

He said while there’s been no contact with the mysterious beings, there’s evidence that they’re using “intelligently controlled vehicles that are highly sophisticated” around US military bases.

Navy pilots told the New York Times that they witnessed “strange objects” reaching heights of 30,000 feet and flying at hypersonic speeds.

“Unidentified: Inside America’s UFO Investigation,” a six-part, one-hour series, premieres Friday.

“We are giving military personnel on the front line a voice,” Mellon said. “We are helping them get out the message of what it is they are encountering and why they are so concerned about it.”

The Post exclusively reported last week that the Pentagon finally admitted it actively investigates sightings of possible alien spacecraft.

And on Wednesday, The Post launched “The Basement Office,” a new video series dedicated to hashing out the UFO phenomenon.