Berlin, September 24 (RHC)-- Volkswagen Chief Executive Martin Winterkorn resigned on Wednesday, taking responsibility for the German carmaker's rigging of U.S. emissions tests.

"Volkswagen needs a fresh start - also in terms of personnel. I am clearing the way for this fresh start with my resignation," 68-year-old Winterkorn, who has been at the helm for eight years.

U.S. authorities are planning criminal investigations after discovering that Volkswagen programmed computers in its cars to detect when they were being tested and alter the running of their diesel engines to conceal the true level of emissions.

Senior members of Volkswagen's supervisory board said in a separate statement they expected further 'heads to roll' in the coming days as an internal investigation seeks to identify who was responsible for what has turned into the biggest scandal in Volkswagen's 78-year history.

Volkswagen said on Tuesday it was setting aside €6.5 billion ($7.3 billion) to help cover the costs of the crisis, though analysts doubt that will be enough.