The chief executive of Volkswagen has apologised over emissions tests in which monkeys and human beings breathed toxic diesel fumes.

Matthias Müller said on Tuesday that the tests, which VW funded along with Daimler and BMW, were “unethical and repulsive”.

The three German car manufacturers have faced widespread outrage, after it emerged that they had funded tests carried out in 2014 via a body called EUGT, which saw 10 monkeys be locked into airtight containers before being made to breathe the exhaust from a VW Beetle. Twenty-five healthy human beings also breathed the fumes as part of the experiment.

Harald Ullmann, a vice president for the animal rights charity Peta, wrote to Mr Müller on Friday to voice anger about the experiments.

“There is nothing fair about condemning these complex, sensitive animals to suffer physical suffering and psychological torment in laboratories where they are caged and deprived of fresh air, sunshine, freedom of movement, the companionship of others and just about everything else that makes any life worth living,” he wrote.

Barbara Hendricks, the German environment minister, described the experiments as “abominable”.

Acting transport minister Christian Schmidt said he strongly condemned the tests, adding: “This has once again damaged trust in the auto industry.”

“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 spokesperson Steffen Seibert told a news conference in Berlin.

The tests were aimed at countering allegations that diesel emissions, which have been linked to asthma, lung diseases and heart attacks, were harmful to health.

The details of the experiment were disclosed in legal action brought against Volkswagen in the United States.

Members of Volkswagen’s supervisory board have called for an inquiry into the tests, German media reported on Monday.

It remains unclear whether the manufacturers were aware of monkeys being used in the experiments.