European Union foreign affairs chief Federica Mogherini says she is preparing to visit Iran following the implementation of a landmark nuclear deal between Tehran with world powers.

Mogherini said Saturday there was no set date had been set, but that preparations with Tehran were well underway. She insisted all 28 EU nations were backing the opening with Iran.

Speaking after a meeting of EU foreign ministers, she said: "It was very important to see the unity of the member states in the direction, intentions and preparations of this work we are doing with Iran."

Mogherini said she would also host her Iranian counterpart in Brussels around the middle of the month.