Volkswagen's supervisory board has reportedly called for an immediate inquiry into who within VW ordered scientific tests in which monkeys were exposed to harmful diesel fumes as reports in Germany say that humans have also been subject to tailpipe emissions testing.

 "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. "Whoever is responsible for this must of course be held accountable," he added, according to Reuters.

The New York Times has reported that German carmakers used the European Research Group on Environment and Health in the Transport Sector (known as EUGT) to commission tests on monkeys. It said the EUGT study, conducted in 2014, was designed to defend diesel following suggestions that the fuel's exhaust fumes were carcinogenic, the NYT reported. VW has subsequently been found to have cheated on diesel emissions tests in the US – the vehicles putting out more toxic pollutants than the official tests showed.

The report also said that the EUGT received study funding from Volkswagen, Daimler and BMW and that monkeys were used in the experiments.

German daily Stuttgarter Zeitung has also reported that EUGT sponsored scientific studies testing nitrogen dioxide, a gas found in exhaust fumes, on people. The newspaper said around 25 healthy young people inhaled nitrogen dioxide in varying doses over a period of hours at an institute belonging to Aachen University.

Reuters reported that the German government said on Monday that any auto emissions testing on monkeys or people were unjustifiable.