BERLIN: A member of Volkswagen's supervisory board said Thursday that he expects further resignations at the German automaker in the wake of the scandal over rigged US emissions tests.

Olaf Lies, economy and transport minister of VW's home state Lower-Saxony, which holds a 20 percent stake in the company, said the investigation into the scandal was only just starting.

"There must be people responsible for allowing the manipulation of emission levels to happen," he told rbb-Inforadio Thursday.

Lies spoke a day after Volkswagen CEO Martin Winterkorn resigned and said he took responsibility for the "irregularities" found by US inspectors in VW's diesel engines. Winterkorn insisted, however, that he'd personally done nothing wrong.

VW has filed a criminal complaint with German prosecutors, seeking to identify those responsible for any illegal actions in connection with the scandal.

The US Environmental Protection Agency disclosed Friday that stealth software makes VW's 2009-2015 model cars powered by 2.0-liter diesel engines run cleaner during emissions tests than in actual driving.

The EPA accused VW of installing the so-called "defeat device" in 482,000 cars sold in the United States. VW later acknowledged that similar software exists in 11 million diesel cars worldwide and set aside 6.5 billion euros ($7.2 billion) to cover the costs of the scandal.

It is not clear whether cars that had this software would have led them to cheat on emissions tests outside the US as well.

Germany's transport minister this week set up a commission of inquiry to look into the scandal. The motor transport authority is conducting static and road tests on Volkswagen models and spot tests on cars made by other manufacturers, German and foreign.

Transport minister Alexander Dobrindt says the company has told officials that the vehicles in question included cars with 1.6-liter and 2-liter diesel engines in Europe.

Minister Alexander Dobrindt said authorities would continue working with Volkswagen to determine what cars exactly are involved, and it's not yet clear how many of the 11 million are in Europe.