"The position of Mueller has never been up for discussion," a spokesman said in response to questions from Reuters on Tuesday. "Any speculation to the contrary is without foundation and is emphatically rejected."

He said the investigation into the emissions scandal led by U.S. law firm Jones Day had made "considerable further progress" in past weeks and VW should be able to provide a "substantial report" on the matter at the Apr. 21 annual shareholder meeting.

Germany's Bild am Sonntag weekly newspaper had reported that doubts were growing among board members, most notably VW's powerful labor representatives, over Mueller, who took the helm at Volkswagen last September.

(Reporting by Andreas Cremer; Editing by Georgina Prodhan)