Audi, which is the biggest contributor to Volkswagen's (>> Volkswagen) profit, admitted in November 2015 that its 3.0 litre V6 diesel engines were fitted with a device deemed illegal in the United States that allowed cars to evade emissions limits.
Prosecutors had raided Audi last March to investigate who was involved in the use of any illicit software used in the affected 80,000 VW, Audi and Porsche cars in the United States.
And last week, they searched the homes of several current and former Audi employees.
Now the probe into suspected fraud and illicit advertising relates to a total of at least 210,000 vehicles with 3.0 litre engines sold in Europe as well as the United States since 2009, the Munich prosecutors' office said on Tuesday.
The searches at Audi's Ingolstadt headquarters and its factory in the southwestern German town of Neckarsulm included the offices of management board members and the technical development department, Audi said, adding it was cooperating with the authorities.
Prosecutors also searched a private home in the German state of Baden-Wuerttemberg, where the Neckarsulm plant is located, the prosecutors' office said.
The number of suspects identified in connection with the sale of cars in the United States has risen to 14, the prosecutors' office said, up from 13 last month.
The pool of suspects does not include any current or former Audi executives, it said, adding that it is seeking to levy fines against unidentified board members and Audi itself.
(Reporting by Maria Sheahan and Irene Preisinger; Editing by Louise Heavens and Alexander Smith)
By Maria Sheahan and Irene Preisinger