Image copyright AFP Image caption Mr Piech (right) had criticised VW's chief executive in an interview

The chairman of the carmaker Volkswagen (VW), Ferdinand Piech, has resigned after a power struggle with chief executive Martin Winterkorn.

Mr Piech had criticised his chief executive in an interview with the German news magazine Der Spiegel, but did not specify the issue at stake.

Mr Winterkorn has been widely tipped as VW's next chairman. Mr Piech and the Porsche family control 51% of VW.

Volkswagen is the biggest car manufacturer in Europe.

On 17 April, Volkswagen's five-member governing board gave its backing to Mr Winterkorn.

Board member Wolfgang Porsche, a cousin of Mr Piech, said he had given his "personal opinion" without clearing his remarks with other family members.

Mr Piech, 78, is a former VW chief executive. His wife Ursula has also resigned her seat on the board.

"The members of the steering committee came to a consensus that, in the light of the past weeks, the mutual trust necessary for successful cooperation was no longer there," the board said a statement.

The carmaker added that deputy board chairman Berthold Huber would serve as interim chairman.

"The uncertainty had to be ended today," said Mr Huber. "The steering committee was and is conscious of its responsibility to Volkswagen and its many thousand staff."

'Seismic shift'

During his eight-year tenure as chief executive, Mr Winterkorn has overhauled VW and made it one of the world's most successful carmakers, industry analysts say.

He had been seen as a close ally of Mr Piech until relations became strained, reportedly over difficulties in breaking into the lucrative US market.

"Mr Piech's departure represents a seismic shift in Volkswagen's power structure, and could foretell drastic changes in how one of the world's largest automakers operates," said Karl Brauer at automotive research group Kelley Blue Book.

In 2014, VW was the world's second-biggest carmaker by sales, behind Toyota and ahead of GM.

Apart from Volkswagen, the group's brands include Audi, Porsche, Lamborghini, Bugatti, Bentley, Skoda and Seat.