One Week Visit by Huge Saucer over Korea

I'm suprized not to have found this sighting on any calender of UFO events, but it was widely seen by public and military, and it was published in an English language edition of some local newspaper in Tokyo/Yokohama, Japan. 
I was working in Army  Headquarters in Yokohama Japan, message center.  For a period of 4 days a saucer was seen directly over the 38 parallel in Korea.  The military had it on radar and said it's altitude was 40,000 feet. People at that point could see it from the ground. 
After 4 days air force jets were sent up to get a closer look, but not to fire at it.  As they reached about 20,000 feet, the saucer lifted up to 80,000, an altitude that the jets could not achieve. 
It stayed at that altitude for another 3 days.  It was calculated to be 900 feet across -- and then just disappeared.  How can government deny existance of such info.  It's said that anything they can't control is a threat and denied.
Witness indicates that the date of the incident is approximate.  We would welcome reports from any other witnesses to this event.  PD