US President Donald Trump said he has heard "interesting" things about Roswell, the crash site of an alleged UFO.
Mr Trump made the comments in an interview with his son, who asked if the White House incumbent could "let us know what's really going on".
"I won't talk to you about what I know about it, but it's very interesting," he replied.
The Father's Day-themed interview was hosted by the president's reelection campaign.
In 1947, a rancher discovered unidentifiable debris in his sheep pasture outside Roswell in New Mexico.
Air Force officials said it was a crashed weather balloon, but sceptics questioned whether it was in fact at extraterrestrial flying saucer.
10 things we've mistaken for UFOs
10 things we've mistaken for UFOs
This UFO-shaped cloud caused a stir in China when it was spotted hovering in the sky above Jilin Province. The 'lenticular cloud' was pictured moving fast near the Changbai Mountain at the boundary of China and North Korea. After two minutes it was absorbed into a huge cloud cluster and disappeared.
Yes, you read that right. In 2011, a man called 999 to report an unidentified flying object above his house in Hertfordshire. He sounded genuinely panicked and told call handlers blazing lights were coming towards him. Two minutes later the man called back when he realised what he saw was the Moon!
A Swedish diving team found a strange object with "rounded sides and rugged edges" at the bottom of the Baltic Sea in 2011. Some believed that a UFO had crashed into the sea, while others speculated it could be the remains of a World War II German anti-submarine device. Most experts concluded it was most a natural geological formation rather than an "anomalous" object.
This picture shows what looks like the incredible moment a 'UFO' hovered over Seattle. It was in fact the unusual cloud formations around the iconic Space Needle appearing to reveal an alien ship in the sky above the city. But thanks to the building's saucer-like shape it made for a convincing UFO snap.
A rare occurence in 2008 saw Venus, Jupiter and a crescent moon appear together in the night sky from Portsmouth. While planets have been mistaken for UFOs, experts say the sighting was a 'conjunction'. Robert Massey of the Royal Astronomical Society told the Daily Telegraph that "they just appear close in the sky". He added: "I wouldn't be surprised at all if the... police and the [Ministry of Defense] and the [Royal Air Force] get calls about UFO sightings. Because it's a spectacular sight and quite unusual and I think for that reason people really will be struck by it."
Weather balloons are often mistaken for unidentified objects but when they explode they can really look like something that occurs deep in space. When a man from California was scanning the night sky and saw a sudden burst of light through his telescope he was convinced he'd seen a UFO. "I saw another object orbiting this - whatever it was up there, and I’ve never seen anything like that before," Elijah Prychodzko told CBS13. He sent it to a scientist who concluded it was a weather balloon exploding. It was explained as decreasing air pressure causing the rising balloon to expand until it bursts.
Light bouncing off our camera lenses can cause a flare that shows an otherworldly object in our photos and if well placed they can look like alien spacecrafts, like this lens flare that could be a spaceship following a car.
A series of bizarre lights were spotted shining in the sky over Cincinnati in 2012. They were compared to the 1997 Phoenix Lights and after various sightings it was soon revealed that they were not space invaders, but just a group of five skydivers wearing illuminated clothing and performing a pyrotechnics show at a high school event.
These unmanned objects are often deliberately created to look like UFOs to fool people, such as when pizza company Domino's' launched the remote-controlled 'Domicopter'. With more drones in the sky, there have been more UFO reports too. A flying object over a Canadian baseball game in 2013 turned out to be part of a marketing campaign from the H.R. MacMillan Space Center and a camera-mounted drone observing a large crowd of protestors in Moscow was identified as police surveillance. Military drones have also been mistaken for mysterious flying machines - residents in Washington D.C. once thought they had seen UFOs travelling along the Capital Beltway.
One of the most mysterious natural phenomena is ball lightning, which is seen as a flash during a storm and is difficult to capture on camera. Scientists have said ball lightning explains many UFO sightings, like when a green object was seen to roll over the mountains over Brisbane, Australia. Astrophysicist Stephen Hughes told the BBC: "If you put together inexplicable atmospheric phenomena, maybe of an electrical nature, with human psychology and the desire to see something - that could explain a lot of these UFO sightings."
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Decades later the US military acknowledged the debris was related to a top-secret atomic project and the UFO theory has flourished.
The president in the past has spoken sceptically about the possibility that there is something out there.
After his father offered that he heard some "interesting" things about Roswell, Mr Trump Jr asked the president might declassify that information someday.
"Well, I'll have to think about that one," the president responded.
Mr Trump also said that he had watched "a couple" of episodes of Netflix show Tiger King.
Joseph Maldonado-Passage, known as Joe Exotic, the star of the popular docu-series, is serving a 22-year prison sentence after he was convicted for hiring a hit man to murder a rival.
Mr Trump said during a press briefing in April that he was unfamiliar with Tiger King, after his son jokingly said on a radio show that he was lobbying the president for a pardon for Exotic.
The president on Thursday did not say when he was considering a pardon but sounded intrigued by the star of the show.
"That's a whole strange deal going on," Mr Trump said.
"I'll tell you that's a strange guy and a lot of strange people surrounding him."