EU foreign affairs head Federica Mogherini said Monday she will go to Iran next month to build on a deal she helped negotiate to end nuclear sanctions against Tehran.

Mogherini last visited Iran in July shortly after world powers -- Britain, China, France, the United States, Russia plus Germany -- agreed to lift damaging sanctions in return for Tehran accepting strict curbs to prevent it acquiring nuclear weapons.

"My next visit will take place on the 16th of April," she said as she went into a meeting of EU foreign ministers.

"We will discuss with the ministers on which grounds, on which issues and sectors to re-engage so as to reopen full relations" with Iran, she said.

Mogherini made no mention of Iranian ballistic missile tests this month which have alarmed many, especially the United States and France which on Sunday warned Iran that it risked new sanctions as a result.

Under the July accord, the lifting of the nuclear sanctions takes place progressively in line with Tehran meeting its commitments.

A key provision allows them to be restored or "snap-back" immediately if Iran is found in breach of the agreement.

The European Union helped mediate the July agreement and Mogherini has been anxious to return to Iran to build on the momentum, both for the sake of bilateral ties but also in the hope of getting Tehran's help in resolving the Syrian and other regional conflicts.