German automakers have confirmed that researchers they commissioned used monkeys to test the health effects of inhaling diesel fumes.

Volkswagen (VLKAF), BMW (BAYRY) and Daimler (DDAIF), the owner of Mercedes, financed a 2014 study in which caged monkeys were forced to inhale fumes from a diesel Volkswagen.

The New York Times first reported on the study last week. The tests are also mentioned in the premier episode of the Netflix documentary series "Dirty Money."

The study was part of an attempt to prove that new diesel engines were cleaner than their predecessors. The test vehicle was rigged to reduce emissions, part of a much bigger scandal that would later cost Volkswagen tens of billions.

"We believe that the scientific methods used to conduct the study were wrong and that it would have been better not to undertake it at all," Volkswagen said in a statement on Monday.

Volkswagen said the study was commissioned by the European Research Group on Environment and Health in the Transport Sector (EUGT), an institute established by the three car makers and parts supplier Bosch.

Tests were conducted by the Lovelace Respiratory Research Institute, which is based in Albuquerque, New Mexico. Volkswagen said the project was "not completed or published" before the EUGT was dissolved in June 2017.

The circumstances of the study, and details on how it was conducted, are contained in a sworn deposition of Jake McDonald, a scientist who oversaw the project.

McDonald said in the deposition, which was taken as part of diesel emissions suit filed against Volkswagen, that the monkeys were shown cartoons during hours of tests to help keep them calm.

The lawyer who conducted the deposition, Michael Melkersen, provided CNN with a copy of the transcript. McDonald did not know when the tests were conducted that the vehicle's emissions were rigged.

Related: Volkswagen used to love diesel. Not anymore

Hans Dieter Pötsch, chairman of Volkswagen's supervisory board, said he would "do everything possible to ensure that this matter is investigated in detail."

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

Daimler said in a statement that it has launched an investigation.

"We are appalled by the nature and extent of the studies and their implementation. We condemn the experiments in the strongest terms," the company said.

Daimler said, however, that all work commissioned with the EUGT was "accompanied and reviewed by a research advisory committee consisting of scientists from renowned universities and research institutes."

Representatives from BMW were not immediately available for comment.

The German government condemned the tests.

'These tests ... are in no ethical way justifiable and they raise many critical questions about those who are behind the tests," said Steffen Seibert, a spokesman for German Chancellor Angela Merkel.

Germany has some of the strictest animal testing rules in Europe. According to the German ministry of food and agriculture, the country has imposed a "near total ban on the use of apes as laboratory animals."

Regulations are more permissive in the United States, where tens of thousands of nun-humane primates are used in experiments each year, according to the U.S. Department of Agriculture.

The Lovelace Respiratory Research Institute confirmed Monday that it conducted the study, but said it would not be published because the research had been compromised by Volkswagen emissions cheating.

It's the latest example of fallout from Volkswagen's bombshell admission in 2015 that it had rigged millions of diesel cars worldwide to cheat on emissions tests.

U.S. prosecutors allege that its engineers knew as far back as 2006 that the company's new 2.0 liter diesel engine would not be capable of complying with regulations.

Related: Volkswagen's diesel scandal costs hit $30 billion

Volkswagen, which owns Audi, Porsche, Skoda and SEAT, resorted to cheating, exposing the industry to charges that dirty diesel engines are to blame for air pollution problems in Europe.

The cars had software installed that strictly limited emissions when the cars were being tested, then dumped up to 40 times the allowable levels of some pollutants when on the road.

As of late 2017, dealing with the scandal had cost Volkswagen a total of $30 billion.

-- Claudia Otto, Nadine Schmidt, Chris Liakos and Charles Capel contributed reporting.