German crime units and prosecutors on Monday searched two Opel offices in the western German cities of Rüsselsheim and Kaiserslautern in the latest probe into alleged fraud over levels of carbon emissions in diesel vehicles.

The Federal Motor Transport Authority (KBA) lodged a case against the car manufacturer in April this year which resulted in a probe overseen by the State Criminal Police Office (LKA) of the federal state of Hesse and triggered by the Frankfurt Attorney.

Prosecutor Nadja Niesen said the investigation was launched due to suspected fraud relating to diesel vehicles currently on the road operating with software that manipulates polluting emissions data.

The transport minister added in a statement that around 100,000 Cascada, Insignia and Zafira Opel vehicles would be called back as part of investigations.

In 2015, shortly after the diesel emissions scandal broke, the KBA found four questionable devices in various Opel cars that manipulated the emissions data being recorded.

Opel launched a voluntary campaign to update the software in affected cars.

In January the KBA detected another device with software to alter emissions controls, which they handed to the state prosecutor in order to launch an investigation.