Functional programming, by definition, is expressing a program as a function to be evaluated. That implies that, at least to some extent, all functional programs are written in a declarative style.

However, we use a declarative style for other kinds of language as well: Prolog, SQL and CSS are three very different examples, none of which is a functional programming language similar to ML or Haskell or Clojure.

declarative vs imperative is kind of a subjective thing but functional programming is not the only way to do declarative programming (logic programming and SQL are two examples that come to mind)