Officials say the mysterious monolith discovered in a remote area of Utah last week has disappeared - cue The X-Files theme tune.
Utah's Bureau of Land Management said it had received 'credible reports' the object had been removed by 'an unknown party'.
In a statement posted on Facebook, the Bureau said: "We have received credible reports that the illegally installed structure, referred to as the 'monolith', has been removed from Bureau of Land Management (BLM) public lands by an unknown party.
"The BLM did not remove the structure which is considered private property. We do not investigate crimes involving private property which are handled by the local sheriff's office.
"The structure has received international and national attention and we received reports that a person or group removed it on the evening of Nov. 27."
Ryan Bacher, a Utah helicopter pilot, told KSL he visited the site on Friday but that when his pal went the next day, it had gone.
The origins of the four-metre (12ft) high metal block are still unclear.
It was first spotted last week, but according to Google Maps has actually been in situ since 2016.
Its discovery has captured people's imaginations as they attempt to come up with a solid theory on how it got there - everything from aliens to a late US sculptor have been credited as being responsible for the bizarre monolith.
In response to its discovery, Utah's Bureau of Land Management said: "Although we can't comment on active investigations, the Bureau of Land Management would like to remind public land visitors that using, occupying, or developing the public lands or their resources without a required authorisation is illegal, no matter what planet you are from."
The Bureau also urged people not to attempt to visit it, saying: "The exact location of the installation is not being disclosed since it is in a very remote area and if individuals were to attempt to visit the area, there is a significant possibility they may become stranded and require rescue.
"We are encouraging anyone who knows the location of the monolith to not attempt to visit it due to road conditions."
People thought the mystery had been solved when gallery owner David Zwirner, who has exhibited the work of late sculptor John McCracken's work since 1997, released a statement claiming it was 'definitely' a secret piece from the artist.
However, a spokesperson from The David Zwirner Gallery, later told Art News: "While this is not a work by the late American artist John McCracken, we suspect it is a work by a fellow artist paying homage to McCracken."