Volkswagen has taken responsibility for diesel emissions tests on humans and monkeys amid mounting fury.
VW chief executive Matthias Mueller said the German car maker had "taken first consequences" for the tests.
He said the animal testing was "wrong ... unethical and repulsive", Spiegel Online reported.
VW has suspended its chief lobbyist Thomas Steg, who admitted to knowing in advance about the monkey experiment, which took place in New Mexico in 2014.
He said "what happened should never have happened, I regret it very much" and took "full responsibility".
The exhaust fume tests were carried out by EUGT, a now disbanded body that had been funded by VW as well as rivals Daimler, which owns Mercedes Benz, and BMW.
Last week the New York Times reported that EUGT had exposed 10 monkeys to fumes - in an air-tight chamber - from several cars, including a diesel VW Beetle, at a lab in Albuquerque.
In his first public comments on the test, Mr Mueller said: "The methods used by EUGT in the United States were wrong, they were unethical and repulsive. I am sorry that Volkswagen was involved in the matter as one of the sponsors of EUGT."
Germany's Stuttgarter Zeitung and SWR radio reported that 19 men and six women had inhaled diesel fumes in another EUGT experiment.
The German government has called a meeting with the car makers to seek an explanation for the experiments, which have been condemned by politicians and animal rights activists.
The controversy follows a scandal over software installed in Volkswagen's diesel cars that enbabled them to appear less polluting during official tests.
In 2015 VW admitted to fitting so-called "cheat" devices and the scandal has cost Volkswagen almost $30bn.
Last month former VW executive Oliver Schmidt was sentenced to seven years in prison in the US and a $400,000 (£293,000) fine after admitting he helped the firm evade clean-air laws.