The German government on Monday dismissed as unjustifiable any auto emissions testing on monkeys or people.

German daily Stuttgarter Zeitung reported at the weekend that a research organisation funded by German carmakers sponsored scientific experiments testing nitrogen dioxide, a gas found in exhaust fumes, on people.

"These tests on monkeys or even people are in no ethical way justifiable and raise many critical questions about those who are behind the tests," government spokesman Steffen Seibert told a regular government news conference in Berlin.

"The supervisory bodies of those who issued these contracts have a special responsibility," he added.

The New York Times reported on Friday that German carmakers had used the European Research Group on Environment and Health in the Transport Sector, also known as EUGT, to commission the study, which was designed to defend diesel following revelations that the fuel's exhaust fumes were carcinogenic.

Reuters could not immediately confirm the details of the study and a representative for EUGT, which was dissolved last year, could not be reached for comment.

EUGT received all of its funding from Volkswagen, Daimler and BMW, the New York Times said. It remains unclear whether the carmakers were aware of monkeys being used in the experiments.

Volkswagen and fellow German carmakers Daimler and BMW on Saturday denounced the study, which was conducted in 2014. Revelations about the study are the latest aftershock from the Volkswagen emissions-rigging scandal, which are continuing to rock the auto industry.

Bernd Althusmann, a member of Volkswagen's supervisory board representing the carmaker's home state of Lower Saxony, said such experiments were "absurd and inexcusable", German news agency DPA reported on Monday.