The US Department of Defense has released three declassified videos of "unexplained aerial phenomena".
The Pentagon said it wanted to "clear up any misconceptions by the public on whether or not the footage that has been circulating was real".
The videos had already been leaked in 2007 and 2017.
Two were published by the New York Times, while the third was leaked by an organisation co-founded by former Blink-182 singer Tom DeLonge.
After they were first leaked, some people claimed the videos showed alien unidentified flying objects (UFOs).
What's in the videos?
According to the New York Times, a clip from 2004 was filmed by two navy fighter pilots and shows a round object hovering above the water, about 100 miles (160 km) out into the Pacific Ocean.
Two other videos filmed in 2015 show objects moving through the air, one of which is spinning. In one, a pilot is heard saying: "Look at that thing, dude! It's rotating!"
In its statement, the Pentagon said: "After a thorough review, the department has determined that the authorised release of these unclassified videos does not reveal any sensitive capabilities or systems, and does not impinge on any subsequent investigations of military air space incursions by unidentified aerial phenomena.
"DOD [Department of Defense] is releasing the videos in order to clear up any misconceptions by the public on whether or not the footage that has been circulating was real, or whether or not there is more to the videos. The aerial phenomena observed in the videos remain characterized as 'unidentified'."
The fascination with the unexplained never goes away. And the UFO phenomenon is perhaps one of the most potent of these stories, linking uncertainty about worlds beyond our own to conspiracy theories about government and especially the US government.
Down the centuries people have looked to the sky and tried to explain mysterious lights and objects. But the modern UFO story took root in 1947 when a farmer discovered debris at Roswell, New Mexico, initially described as a flying disc, but now thought to be part of a secretive balloon programme to monitor the Soviet Union.
Subsequently the testing base for advanced aircraft, known as Area 51 in Nevada, became the alleged centre for UFO research. For the conspiracy theorists this was where the US government sought to harness advanced alien technology.
Over the years many of the most outlandish theories have been debunked. But in 2017, the Pentagon did finally admit that it had a long-standing programme, now terminated, investigating alleged UFOs.
Today, the US Navy prefers to call these unexplained sightings "Unidentified Aerial Phenomena". But that's not going to supplant an acronym which has entered into our collective sub-conscious, prompting that fundamental question: are we really alone in the universe?
Tweeting about the release, DeLonge thanked shareholders in his organisation, To the Stars Academy of Arts and Sciences, and said he was hoping to fund further research into the objects.
"With today's events and articles on my and @TTSAcademy's efforts to get the US Gov to start the grand conversation, I want to thank every share holder at To The Stars for believing in us," he said.
"Next, we plan on pursuing the technology, finding more answers and telling the stories."
The musician co-founded the academy in 2017 in order to study UFOs and other paranormal phenomena.