The New York Times on Friday said German carmakers had used the European Research Group on Environment and Health in the Transport Sector, also known as EUGT, to commission a study created to defend the use of diesel following revelations that the fuel's exhaust fumes were carcinogenic.
After media reports showed that Volkswagen has been complicit in experimenting on monkeys and letting them inhale auto fumes to test the toxicity of diesel emissions, another apology has been promoted from German car-maker.
Over the weekend, German daily Stuttgarter Zeitung reported that EUGT also sponsored scientific studies testing nitrogen dioxide, a gas found in exhaust fumes, on people.
German carmakers on Saturday condemned the use of animals in the experiment.
The German government said on Monday that any auto emissions testing on monkeys or people were unjustifiable.
The New York Timesreported on Friday about a 2014 trial in a USA laboratory in which 10 monkeys inhaled diesel emissions from a VW Beetle.
Daimler said separately it would start an investigation into the study ordered by the European Scientific Study Group for the Environment, Health and Transport Sector.
In an additional twist, the Beetle model used in the test was among the vehicles that were rigged to conform to test limits, The New York Timesreported. Volkswagen apologized for the misconduct and lack of judgment of some individuals, calling the trials a mistake.
"We are appalled by the extent of the studies and their implementation", a Daimler spokesman told AFP, saying the Mercedes-Benz parent "condemns the experiments in the strongest terms".
Reuters could not immediately confirm the details of the study and a representative for EUGT, which was dissolved previous year, could not be reached for comment.
While it was the EUGT that commissioned the tests on humans on monkeys, the organisation itself was financed by the three carmakers hoping its research would defend diesel's environmentally-friendly reputation-and the valuable tax breaks that go with it.
The advisory boards of those, who commissioned the test - Volkswagen, Daimler and BMW - must now answer critical questions on the experiment and its goals, according to the chancellor.
On its website the World Health Organisation points to "growing evidence" that nitrogen dioxide exposure 'can increase symptoms of bronchitis and asthma, as well as lead to respiratory infections and reduced lung function and growth'.
Exposure is "linked to premature mortality. from cardiovascular and respiratory diseases", it states.
Bosch said it left the group in 2013. VW on Monday again distanced itself from the activities of the group.