In what countries does the U.S. have military personnel. Are there any countries where we do not have any?

Question

In particular do we have embassies or bases in Iran, North Korea, China, Cuba?

Answer 1

We have an embassy in China, none in North Korea, Iran or Cuba.

We've got the base at Gitmo we lease from Cuba.

Answer 2

If we have an embassy or legation in a country we have military personnel.  Iran, North Korea and Cuba do not have embassies, China does.  Although we do have a naval base in Cuba.  In addition some third world countries with inimical interests to the US are without one either.