German luxury car maker Daimler, which is being investigated for alleged emissions cheating, announced Tuesday a voluntary recall of over three million Mercedes-Benz diesel vehicles in Europe.

It said it had already launched a voluntary service action for some models and that "in order to effectively improve the emissions of additional model series, Daimler has now decided to extend the service action to include over three million Mercedes-Benz vehicles."

German authorities have been investigating Daimler employees on suspicion of fraud and misleading advertising in relation to the selling of diesel-powered vehicles. Last week it became clear that the investigation involves around more than one million automobiles.

The Daimler probe is part of a wider investigation into the emissions scandal that broke in September 2015 when German carmaker Volkswagen admitted that more than 11 million vehicles around the world had been equipped with special software aimed at cheating emissions test