A view of Volkswagen's booth at the 45th Tokyo Motor Show 2017 in Tokyo in October 2017. Photo: IC

Volkswagen's supervisory board called 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.

"Whoever is responsible for this must of course be held accountable," Poetsch said in response to a New York Times report on Friday that German carmakers had used an organization 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. The group could not be reached for comment.

EUGT received all of its funding from VW and fellow German carmakers Daimler and BMW, the New York Times said.

Representatives of automakers General Motors Co, Ford Motor Co and Fiat Chrysler Automobiles NV said on Monday they do not test the effects of emissions on humans or animals.

Unjustifiable decision

Volkswagen, Daimler and BMW on Saturday denounced the study, the revelation of which was the latest aftershock from the VW emissions-rigging scandal, which continues to rock the auto industry.

Volkswagen has pledged never to test with animals again, Thomas Steg, VW's chief lobbyist, told German daily Bild in an interview on Tuesday.

"We want to absolutely rule out testing on animals for the future so that this doesn't happen again," Bild quoted Steg as saying.

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, were aware of the tests at the time.

Volkswagen said the study was never discussed in any management board meetings, after Bild earlier reported that an internal email showed at least some senior managers were informed about the design of the research.

In a related development, German daily Stuttgarter Zeitung reported on Sunday that EUGT also sponsored scientific experiments testing nitrogen dioxide, a gas found in exhaust fumes, on people.

Aachen University's research hospital confirmed on Monday that EUGT had sponsored a study in 2013 and 2014, but said it was related to workplace safety, not diesel emissions.

As part of the study, 25 people were exposed to varying levels of nitrogen dioxide for three hours to investigate the possible health effects of the chemical compound in concentrations below the limit for workplaces, Uniklinik RWTH Aachen said in a statement.

The German government said on Monday that any auto emissions testing on monkeys or people was unjustifiable.

"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.

Stephan Weil, who represents the German state of Lower Saxony, a VW shareholder on the carmaker's supervisory board, said the board was pressing the carmaker to provide information about the aim of the studies.

"After the matter has been cleared up there will also be the question of who was personally responsible," he said at a news conference on Monday.