The Pentagon has released classified footage filmed from a US fighter jet showing a mysterious flying object over San Diego, California.
In the video, the pilots can be heard reacting with astonishment: “Look at that thing, dude,” one says to the other, “It’s rotating.”
According to the New York Times, the US Department of Defence (DoD) admitted to a secret $22m ($15m) programme that was created to investigate reports of such Unidentified Flying Objects (UFOs).
The Advanced Aerospace Threat Identification Programme looked into what it called "advanced aviation threats" and it ran for five years, from 2007 to 2012.
The programme was the brainchild of Harry Reid, a former US senator.
He told the New York Times:
"I'm not embarrassed or ashamed or sorry I got this thing going. I've done something that no one has done before."
He later tweeted that the programme was about science and national security.
Most of the funding went to a space research company run by the billionaire entrepreneur Robert Bigelow who has said he is convinced that aliens exist.
Earlier this year, the US Central Intelligence Agency (CIA) released millions of pages of declassified documents online, including some from the programme.
These describe sightings of unidentified objects - sometimes filmed by US fighter pilots - speeding through the skies.
However, scientists have stressed that unexplained phenomena are not proof of alien life or interstellar visitors.