BERLIN - Audi chief executive officer (CEO) Rupert Stadler has been taken into police custody in the course of ongoing investigations by German authorities into the "dieselgate" scandal, a spokesperson for the luxury carmaker's parent company Volkswagen group confirmed on Monday.

The Munich II State Prosecution Office responsible for investigations announced that the arrest warrant for the CEO was due to a danger of collusion posed by the suspect.

Volkswagen said it could not comment on the ongoing case but emphasized that Stadler was innocent until proven guilty.

Stadler and another unnamed senior manager at the Volkswagen Group subsidiary were recently officially listed as suspects by state prosecutors in the "dieselgate" scandal. Raids were carried out at both their private residences in an attempt to gather evidence of their involvement in diesel emissions-cheating practices.

Both stand accused of criminal fraud and "indirect false certification" in the European marketing of diesel vehicles which had been fitted with illicit defeat devices to falsify Nitrogen Oxide (NOx) emission levels in test settings.

German investigators believe that the luxury carmaker has sold at least 210,000 diesel vehicles with illegal emissions-cheating software in the United States and Europe since 2009.

According to prosecutors, Stadler must have been aware of the illicit practices following first revelations of a "dieselgate" scandal in the United States back in 2015 but still refused to halt sales of affected vehicles in Europe thereafter. According to the German press agency (dpa), investigators arrived at this conclusion through an assessment of the Audi CEO's written correspondence.

Until Stadler's arrest on Monday, the former head of Audi's engine development division was the only suspect held in police custody in Germany. Investigations were expanded yet again in May after the Federal Motor Transport Agency (KBA) discovered a previously unknown emissions cheating technology in the newest diesel versions of the popular Audi A6 and A7 models.

Stadler subsequently vowed to investors at his company's annual general meeting that Audi and the Volkswagen Group had learned their lessons and would henceforth prioritize "moral and legally proper behavior." Nevertheless, there has been widespread speculation in German media that the "dieselgate" scandal could ultimately cost Stadler his job as part of wider reforms announced by the Volkswagen Group.

The supervisory board of Volkswagen is scheduled to hold a regular session on Monday afternoon, in which new revelations in the "dieselgate" scandal will feature on the agenda.