Volkswagen's supervisory board chief Ferdinand Piech is plotting a new coup to try to oust the German carmaker's chief executive, Martin Winterkorn, Germany's public broadcaster NDR reported on Thursday.

Just days after Piech's previous attempts suffered a severe blow when core supervisory board members said they fully backed Winterkorn and wanted to extend his contract, NDR reported that 78-year-old Piech is trying to drum up a majority on the full supervisory board to have him removed from office.

At the carmaker's annual general meeting on May 5, Piech hopes to secure enough votes to have Winterkorn replaced with either Porsche chief Matthias Mueller or Skoda head Winfried Vahland, the broadcaster said.

VW refused to comment on the report.

"That is speculation which we're not commenting on," a company spokesman said.

Last Friday, the six-member steering committee of VW's 20-strong supervisory board attempted to draw a line under a bitter power struggle between Piech and Winterkorn, insisting that Winterkorn was "the best possible chief executive for Volkswagen" and that his contract should be extended.

The dispute erupted after Piech, a member of the powerful Porsche dynasty that is a shareholder in Volkswagen, and one of the most important figures in German business, sent shockwaves through German industry by declaring in a magazine interview that he was "distancing himself" from Winterkorn.

Until now, Winterkorn had been seen as Piech's close ally and heir apparent and the idea of a poisonous rift between the two ignited fears about the future running of Europe's biggest carmaker, whose empire spans 12 brands and annual sales of 200 billion euros ($215 billion).

The steering committee comprises six of the most influential members of VW's 20-strong supervisory board, including the head of the general works committee, the head of the mighty IG Metall metalworkers' union and the head of the regional state of Lower Saxony where the carmaker is based.

Piech is the grandson of the inventor of the iconic Beetle, the model on which VW's fortune was built, and was himself VW's chief executive between 1993 and 2002, before becoming its supervisory board chief.

He is also one of the representatives of the Porsche family, whose holding company Porsche SE holds nearly 51 percent of VW.

It was Piech who installed Winterkorn as chief executive in 2007.

But he appears to have become irked by his former protege's difficulties in making substantial inroads into the US market, as well as VW's over-dependence on the Chinese market and the waning attractiveness of its core Volkswagen brand.