On Friday, prosecutors said they would look into possible cheating by Renault, after independent French experts found dangerously high levels of emissions from diesel engines of several carmakers.

Renault insisted its engines complied "with French and European regulations", adding that its vehicles did not have software allowing it to commit fraud in this area.

Three judges have been looking into the Renault matter, a source told Reuters. Whether the prosecutor's inquiry is followed by a trial is for the judges to decide. They are focused on the public health implications of Renault's actions.

The probe follows the Volkswagen diesel emissions scandal, which emerged in September 2015.

Just a day after US officials said VW would plead guilty to three criminal charges and pay a total of $4.3 billion in fines to settle its scandal, the US Environmental Protection Agency charged that Fiat Chrysler had hidden software on diesel trucks that allowed them to spew out excess emissions.

For its part, Fiat Chrysler also denied the charges and pledged to work with President-elect Donald Trump's adminstration to resolve the issue "fairly".

The EPA said undisclosed software on the 2014 to 2016 models of Grand Cherokees and Dodge Ram 1500 trucks sold in the United States allowed the vehicles to emit more nitrogen oxides than permitted.

Inquiries into diesel emissions will impact automotive stocks in the near term, said Terry Torrison, managing director at Monaco-based McLaren Securities.

“Every regulator seems to have a bee in their bonnet about diesel emissions. This story is not going to go away any time soon," Torrison said.

- News24.com