Volkswagen today rejected investor calls for the carmaker to publish the results of a key investigation into its diesel emissions cheating scandal, saying it was unable to do so for legal reasons.

Investment advisory firm Hermes EOS said on Tuesday the findings of a company-commissioned probe by US law firm Jones Day should be disclosed, and would allow Volkswagen to move on from its biggest-ever corporate crisis.

"There is no written concluding report by Jones Day and there will not be one," VW Chairman Hans Dieter Poetsch said at the company's annual shareholder meeting.

"I ask for your understanding that VW for legal reasons is prevented from publishing such a final report," he told the gathering of about 3,000 shareholders.

VW initially pledged to inform shareholders about the findings of the Jones Day report which was used as the basis for a $4.3 billion settlement with the U.S. Justice Department, but has since abandoned this plan.

It says the report was incorporated in the "statement of facts" published by the Justice Department, and that as part of the settlement deal it cannot publish separate findings.

One shareholder, however, criticised this explanation.

"Your reference to the statement of facts agreed in the US is completely insufficient and almost insulting to all those who are interested in complete clarification of responsibilities," said Christian Strenger, supervisory board member at DWS Deutsche Asset Management GmbH.

Chief Executive Matthias Mueller said VW would support without reservation Larry Thompson, a former US deputy attorney general, who has been picked by the Justice Department to oversee the world's largest automaker for three years.

Thompson and his team will have access to VW documents and assess the efforts of its board of management and senior management to comply with environmental laws.

In total, VW has agreed to spend up to $25 billion in the United States to address claims from owners, environmental regulators, states and dealers and offered to buy back about 500,000 polluting US vehicles.

"I see this as an opportunity," Mueller said. "The work of the monitor can and will contribute to bringing risk management, compliance and integrity within the group to new levels."