BERLIN— Volkswagen AG Tuesday suspended a senior executive amid mounting outrage over revelations this week that the car maker had conducted experiments on animal and humans in an effort to disprove links between diesel fumes and respiratory illnesses.

The experiments were carried out in 2013 by a laboratory in the U.S. and commissioned by a European research group owned by Volkswagen, BMW AG and Daimler AG , the maker of Mercedes-Benz cars.

On Thursday, the New York Times reported the monkey experiments but added that a VW Beetle used for it was in fact rigged so that the animals were exposed to less concentrated fumes than advertised.

In an unrelated experiment, 25 people were connected to respirators and breathed a concentration that included nitrogen oxide, or NOx, the toxic particle contained in diesel emissions.

The revelations sparked an uproar in Germany over the use of animals and humans in dubious tests that appeared aimed at fooling the public to believe diesel emissions posed no public health hazard. They have plunged the auto companies into a public relations crisis and subjected them to harsh criticism from government officials and animal rights advocates.