BERLIN, April 18 (Xinhua) -- German state prosecutors and regional police have searched several premises associated with the car makers Porsche and Audi in the ongoing "dieselgate scandal", a spokesperson for the Stuttgart State Prosecution Office confirmed on Wednesday.

The spokesperson told press that Stuttgart-based Porsche and Ingolstadt-based Audi were being investigated for potentially committing criminal offenses of fraud and illicit advertising in connection to diesel emissions cheating practices. Three Porsche employees, including one member of the management board, have been formally listed as suspects in the case by German judicial authorities.

Reacting to the incident on Wednesday, a Porsche spokesperson said investigators had examined and secured documents at corporate premises.

Porsche and Audi, both of which are subsidiaries of the larger Wolfsburg-based Volkswagen Group, are being targeted in a joint investigatory effort by state prosecutors in the "dieselgate" scandal. The spokesperson said the two firms were fully cooperating with the authorities.

Around 30 state prosecutors, as well as 160 officers have joined forces to shine a light on Porsche and Audi's potential involvement in the installation of illegal software which understated nitrogen oxide (Nox) emissions levels produced by diesel vehicles including the Porsche "Cayenne".

Audi was responsible for delivering large six-cylinder diesel motors to Porsche used in the "Cayenne" SUV of the brand.

The Stuttgart State Prosecution Office noted that Audi premises in Ingolstadt and in Neckarsulm were also searched, but did not provide any additional information to press. A spokesperson merely said that investigators were trying to secure more evidence to assist ongoing investigations.

Porsche has voluntarily ordered recalls of its Macan SUVs following reports that diesel versions of the model emitted significantly more NOx than is permissible under European Union (EU) clean air regulations.

The German ministry for transport subsequently ordered a formal ban on new registrations for Porsche "Cayenne" cars with 3.0-liter diesel motors.

So far, Porsche and Audi's mother corporation Volkswagen has paid out more than 25 billion euros (31 billion U.S. dollars) in settlements and fines as a result of the "dieselgate" scandal since 2015 in the United States alone.

The Braunschweig State Prosecution Office is currently investigating senior Volkswagen managers on suspicion of market-manipulation offenses committed by the publicly-listed car maker.