Munich - Guillaume de Posch, the chief executive at the biggest of Germany's four main television groups, ProSiebenSat. 1, resigned Tuesday in an unexpected move that sent the group's shares lower.

The group is controlled by two private-equity investment companies, KKR (Kohlberg Kravis Roberts) and Permira, and has 3.5 billion euros (5.4 billion dollars) in debt after its takeover last year of Swedish based TV group SBS.

ProSiebenSat. 1 said de Posch was leaving at his own wish, effective at the end of this year, as it was the right time to move on, but gave no reason for his departure. He has run the group for the past four years.

A successor would be chosen over the next few months so there was an orderly transfer of control, a company spokesman said.

Shares in the company, which are tracked in the M-DAX index, fell 3.5 per cent to 7.42 euros as investors took stock of the change.

ProSiebenSat. 1 is up against two public groups, ARD and ZDF, and another commercial broadcaster, RTL, in the competition for advertising spending in Europe's richest single television market. (dpa)