Object performed impossible maneuver at extreme altitude

Flying out of Kadena, Okinawa, on a high-speed, high-altitude recon mission, encountered an unknown object appx ten meters in length, and appx three meters in height.  
There was a firm, sharp outline of the craft silhoutted against the sky.  
Performed evasive maneuvers, and the 'birdwatcher' tattled on me.  
Object stayed on starboard side regardless of maneuvers.  
After appx six to eight minutes of this, the craft accelerated over the horizon in less than five seconds.  This was an  impossible maneuver since I was at an extreme altitude.  There is no way that a human could withstand the 'G' forces this would have generated.  
Reported incident to CO upon return to base, and nothing else was heard of it.