Volkswagen's supervisory board is calling for an immediate inquiry into who commissioned tests in which monkeys were exposed to toxic diesel fumes, while the German government said such studies were unjustifiable.
"I will do everything possible to ensure that this matter is investigated in detail," Volkswagen supervisory board chairman Hans Dieter Poetsch said in a statement on Monday (local time).
"Whoever is responsible for this must of course be held accountable," Mr Poetsch said in response to a New York Times report on Friday that German car makers had used an organisation called European Research Group on Environment and Health in the Transport Sector (EUGT) to commission the tests.
The study, conducted in 2014, was designed to defend diesel following revelations that the fuel's exhaust fumes were carcinogenic, the newspaper reported.
Reuters could not immediately confirm the details and purpose of the study and EUGT, which was dissolved last year, could not be reached for comment.
EUGT received all of its funding from VW and fellow German car makers Daimler and BMW, the New York Times said.
Volkswagen, Daimler and BMW on Saturday denounced the study, whose revelation is the latest aftershock from the VW emissions-rigging scandal, which continues to rock the auto industry.
On Monday Volkswagen said that some staff members, whom it did not identify, including some in its legal department, at the VW brand's technical development division and at Volkswagen of America, had been aware of the tests at the time.
But Volkswagen said the study was never discussed in any management board meetings, after German daily Bild earlier reported that an internal e-mail showed that at least some senior managers were informed about the design of the research.
The German government said on Monday that any auto emissions testing on monkeys or people were unjustifiable.