Japanese authorities are investigating the origins of a mysterious iron ball that washed up on a Hamamatsu City beach.

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The orb, which measures nearly 5 feet in diameter, prompted police to close off Enshu beach out of fears it could be a mine or other explosive device, but an X-ray of the ball determined it was hollow.

Two raised handles on the surface of the ball led to speculation it could be a mooring buoy that came loose and floated away from its intended location.

Police said the Japanese military and coast guard are reviewing photos of the object in an attempt to identify it.