The Last Grenade(1970)
Two soldiers of fortune, Harry Grigsby and Kip Thompson, used to be the best of friends when they fought side by side in the Congo. But now Kip has changed sides and Grigsby does not forgive him for what he regards as a betrayal, all the more as Thompson now turns his guns against Grigsby's troops and, accordingly, against his former friend. While he is London recovering from tuberculosis, Rigby is assigned a new mission that he gladly accepts: to eliminate Thompson, now in Hong Kong causing tensions with neighboring China by creating border incidents...
This is the theatrical trailer for the movie.