The search included VW's Wolfsburg headquarters, along with Audi's Ingolstadt and Neckarsulm factories and six other unspecified sites, the group said.
"The path towards clearing up (the emissions scandal) is far from over", Audi CEO Rupert Stadler said on Wednesday.
"There is suspicion that devices were built into these vehicles to manipulate emissions readings and conform to USA emissions limits, without the buyers being informed", they continued.
The engine is said to be used in several auto models of VW, Audi as well as Porsche.
"We will keep at it until this work is done", CEO Stadler said.
Audi was the second-largest contributor to VW group sales a year ago, the company's annual report indicated Tuesday, with 1.5 million units sold and €59.3 billion in revenues generated.More news: Scotland Wants Another Vote for Independence Before Brexit
Cars sold in European markets are outside the scope of the investigation, the prosecutor said. The raids took place on the same day as the Audi's annual earnings press conference.
German daily Sueddeutsche Zeitung noted that the prosecutors had learned of the gathering at a time when it was too late to adjust the schedule of the search, which implies that the coincidence was entirely unintentional.
"There is still a long way to go before (dieselgate) is finally cleared up", Stadler told journalists at the firm's annual results press conference today. Audi declined to comment on the probe.
Separately, sales chief Dietmar Voggenreiter played down a 24-percent plunge in two-month Chinese deliveries as temporary, reflecting uncertainty among dealers about the implications of a new joint venture agreement.
Volkswagen and Audi brand vehicles with diesel engines make up the bulk of the vehicles caught up in Volkswagen's emissions cheating scandal. However, German prosecutors said they were not investigating specific Audi managers, with the charges leveled at persons unknown so far.
The prosecutors' probe also adds to Audi's woes as it has been losing ground to Daimler's Mercedes-Benz, which replaced BMW's namesake brand as the world's bestselling premium-car maker past year.