US authorities are investigating Bosch over its role in VW's diesel emissions scandal according to a Reuters report.

The report says that federal prosecutors with the US Department of Justice are examining whether Bosch knew or participated in Volkswagen's efforts to circumvent US diesel emissions tests. The report cited anonymous sources 'familiar with the matter'.

Bosch is a key supplier of component in the diesel engines used in the VW Group models affected.

The report said the probe into Bosch is at an early stage and there is 'no indication of wrong doing'.

Reuters noted that Bosch provides the engine control module, called EDC17, and basic software for nearly all the four-cylinder diesel cars sold in North America, including by VW, BMW and Daimler.

Bosch could face charges if it emerges that it knew its technology was being used by VW to cheat on emissions requirements. However, it is far from clear what role Bosch played in the affair.

Bosch told Reuters previously that the company supplies components such as engine management systems to automakers' specifications, and that "how these components are calibrated and integrated into complete vehicle systems is the responsibility of each automaker."