German prosecutors say they have widened their investigation of Volkswagen to include suspicion of tax evasion after revelations that some of its cars were emitting more carbon dioxide than officially reported.

Braunschweig prosecutor Birgit Seel told The Associated Press on Tuesday that the investigation was focused on five Volkswagen employees but would not release their names.

The focus of the investigation is on tax breaks Volkswagen received for producing low-polluting cars that it might not have qualified for if the emissions were correctly reported, Seel said.

Volkswagen has acknowledged it produced 11 million vehicles worldwide with small diesel engines that contained software allowing them to cheat nitrogen oxide tests. Earlier this month, it also said it found "unexplained inconsistencies" in emissions from more of its vehicles of carbon dioxide.