They are not "Supremecist", but racist, none the less.
Take a look at their theology. Nation of Islam belief is that Blacks are the only true humans, that whites and browns are the result of an evil genetic experiment by an ancient Black scientist called "Yacub". What logicly follows is that whites are to be ultimately exterminated.
The only difference between Nation of Islam and the Nazis is that NoI is not in any position (yet) to take action on their beliefs