By Todd Buell 

FRANKFURT--The powerful chairman of Volkswagen AG unexpectedly resigned Saturday, opening a new period of uncertainty for the automotive giant just weeks after he threw the company into a management crisis by withdrawing his support for VW's chief executive.

Ferdinand Piech "has announced his resignation with immediate effect from his position as Chairman as well as member of the Supervisory Board, as well as all other mandates within the Volkswagen Group," said the Wolfsburg-based company.

Mr. Piech remains one of the company's largest shareholders.

The statement said that Mr. Piech's wife Ursula had also announced her resignation "from all mandates within the Volkswagen Group."

"The deputy Chairman of the Supervisory Board, Berthold Huber, will temporarily assume leadership of the Board until the election of a new Chairman," said the firm.

For the past two weeks, Mr. Piech had been in open conflict with Chief Executive Martin Winterkorn, though late this week had voiced support for him.

Write to Todd Buell at todd.buell@wsj.com

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