BRUSSELS (Reuters) - The head of the European Union's foreign service, French diplomat Alain Le Roy, has resigned after differences with EU foreign policy chief Federica Mogherini, EU diplomats said.

Le Roy's departure "for personal reasons" just 16 months after he took the job of secretary-general of the European External Action Service was disclosed in a brief statement on Wednesday evening announcing the appointment of his successor.

Mogherini named Helga Schmid, 55, a German diplomat who has been political director of the EEAS in charge of issues such as the Iran nuclear negotiations for the last six years, to succeed Le Roy from Sept. 1.

Le Roy was the second senior official in Mogherini's entourage to be eased out within weeks after her first chief-of-staff, Stefano Manservisi, a career heavyweight in the European Commission, was moved to run the EU's international development department in May.

He was replaced by Italian Socialist Fabrizia Panzetti, a long-time personal friend and political associate of Mogherini.

An EU diplomat familiar with the situation said both changes reflected a drive by Mogherini, who was Italian foreign minister before moving to Brussels, to take personal charge of policy and leave others to run the bureaucracy.

Le Roy, a seasoned French, EU and United Nations troubleshooter, had been frustrated because he sought to have a greater input on policy but was expected to "run the machine", the diplomat said.

(Writing by Paul Taylor; Editing by Alastair Macdonald)