Greece's second-largest lender by assets said in a filing to the Athens bourse that the end of Fragiadakis' term coincided with the completion of the main part of the restructuring plan he has overseen.

With the bank now planning to redesign its business strategy, Fragiadakis decided to step down, it said, adding it would now start looking for a successor.

NBG said deputy Chief Executive Paul Mylonas would act as CEO until a shareholders meeting approved a new board. It did not say when that meeting would take place.

NBG said last week it would press on with plans to sell its wholly-owned insurance subsidiary Ethniki Insurance, after a deal to sell 75 percent of the business turned sour earlier this year.

NBG put the insurance unit up for sale as part of a restructuring plan approved by the European Union to exit non-banking operations.

The European Central Bank is due to issue the results of stress tests - a financial check up - of Greece's four systemic banks on Saturday, which includes NBG.

(Reporting by George Georgiopoulos and Angeliki Koutantou; Editing by Jane Merriman and Mark Potter)