It was an older movie I watched on TV in the US, probably around mid-80s, but the movie was obviously much older. It had the same cinematic feel as Invasion of the Body Snatchers. I'm pretty sure it was a legit movie and not a "made for TV" movie.
A creature was created in a lab (I think by accident). It was shaped like a fried egg (mostly flat with a hump in the middle). And I'm 75% sure it also had a single eye stalk; think the trash compactor monster from Star Wars: A New Hope.
Only one was created but it reproduced by splitting. I recall a scene where one was cut in half by an axe, but just became two monsters.
The part I remember for sure is at the end, they managed to stop/kill all the monsters, and the hero stated something to the effect of, "Thank goodness this happened on this isolated island. I couldn't imagine what would happen if this happened on the mainland." The scene then fades to a stock image of a laboratory, and you hear someone talking in Japanese (not English with an accent, but the actual language). They seemed to be talking excitedly, and then the screaming starts, I'm sure to imply that these scientists created the same thing, but now in a major metropolitan area.