CNP Assurances's board appointed deputy CEO Antoine Lissowski to replace Lavenir, who has said he would leave the company on Aug. 31 citing personal reasons. Lissowski will take over on Sept. 1.

"Antoine Lissowski will remain in his temporary position until a new CEO is appointed," the company said, adding it hired a head hunting firm to help find the new CEO.

French state-owned financial firm Caisse des Depots et Consignations is considering selling its 41 percent stake in CNP Assurances to state-owned La Poste, a source close to La Poste said earlier this month.

La Poste would then merge its bank, La Banque Postale, with CNP Assurances to expand the range of services it provides.

The French government, which owns both CDC and La Poste, wants to build up a state-owned company that would provide both banking and insurance services in the country's rural areas which are often neglected by private companies.

(Reporting by Inti Landauro; Editing by Bate Felix and Jane Merriman)