BERLIN/FRANKFURT (Reuters) - Daimler (>> Daimler AG) on Tuesday announced the surprise resignation of Andreas Renschler, head of manufacturing at Mercedes-Benz Cars, in a move that tightens Chief Executive Dieter Zetsche's grip on the company.

Renschler, who is leaving the company of his own accord and with immediate effect, took on his job in April as part of a broader executive reshuffle which saw Zetsche's contract extended by only three rather than five years.

"I very much regret that he is leaving the company for personal reasons," Zetsche said in a statement which also announced that Markus Schaefer, previously head of production planning at Mercedes-Benz Cars, would take on most of Renschler's responsibilities.

Zetsche remains head of Mercedes-Benz Cars, a division which includes luxury cars and the Smart brand.

The issue of succession at Daimler won't become acute until closer to 2016, when Zetsche's contract expires, but Renschler's departure removes one candidate who might have succeeded him.

A company spokesman said Renschler left for purely personal reasons.

Arndt Ellinghorst, an analyst at ISI Group said: "Given Renschler left of his own will, it needs to be seen where he turns up next. Maybe the right man to sort out Volkswagen Group's trucks assets."

Daimler had forced Renschler, who was previously head of Daimler trucks, to switch jobs with Mercedes-Benz production and purchasing chief Wolfgang Bernhard, in a move that would allow both men to showcase their potential.

Bernhard is still seen as a contender to get the top job at Daimler but his tough management style has met resistance among members of the company's powerful labour unions, which control half the seats on the supervisory board.

"The latest move means Zetsche's position is uncontested," a Daimler staffer, who declined to be named, said on Tuesday.

Daimler narrowed a sales gap with its German premium-car rivals BMW (>> Bayerische Motoren Werke AG) and Volkswagen's (>> Volkswagen AG) Audi last year, thanks to a spate of redesigned compact vehicles. The Stuttgart-based manufacturer dropped to third place in the luxury-sales race behind Audi in 2011.

(Reporting by Edward Taylor, Ilona Wissenbach and Andreas Cremer; Editing by Alistair Lyon)

Stocks treated in this article : Bayerische Motoren Werke AG, Daimler AG, Volkswagen AG