Sitting motionless in the sky above the Kremlin in Moscow, clips of the unexplained object have become the most-viewed videos on Russia's YouTube.
The two videos, one taken at night from a car and one during the day, were both filmed by amateurs.
The UFO hovered for hours over Red Square in the Russian capital and was seen by hundreds of people.
The identity of the shape has not been confirmed but internet forums are buzzing with the sighting.
The UFO appeared on December 9th, the same night that a mysterious blue spiral light appeared over Norway. That was later attributed to a failed rocket launch from Russia.
Some have likened the object to one of the spaceships from Star Wars.
But others have said it is merely a reflection from inside the cameraman's car. If the object exists experts estimate that it could be up to a mile wide.
Some commentators have reacted sceptically to the videos and have pointed out that if hundreds of people had seen the object more videos and photos would have emerged by now.
Russian reports ruled out a UFO but police have refused to comment.
Nick Pope, a former Ministry of Defence UFO analyst, said it was 'one of the most extraordinary UFO clips I've ever seen'.
'At first I thought this was a reflection but it appears to move behind a power line, ruling out this theory.'
A spokesman for aerospace journal Jane's News said: 'We have no idea what it is.'