Renault shares plummet more than five percent on Thursday after the company refused to acknowledge reports that it cheated on emissions tests for decades. The automaker calls the media reports unbalanced and denied any wrongdoing on their part.

A French media reported that the country's fraud watchdog believes that Renault distorted the results of an anti-pollution test over a period of 25 years. Investigators say that CEO Carlos Ghosn should be held responsible. Investors sent shares down by 10 percent since the reports were first published. Renault, on the other hand, denied the claims saying it did not cheat on the emissions tests.

"Renault vehicles are not equipped with cheating software affecting anti-pollution systems," the automaker said in a press release statement.

French prosecutors opened an investigation, last January, into allegations of emissions cheating but have not announced any findings. The group also refused to comment on the current investigation since it doesn't have access to the case yet.

But Renault vows to comply with the regulations and reserves its explanations before the Judges in charge of investigating the case. It reminds that none of its services has breached European or national regulations related to vehicle emissions. The automaker fully intends to cooperate with the Judges in the context of the investigation.

Meanwhile, the Renault-Nissan Alliance is the world's fourth-biggest automaker in terms of sales. The company says it had delivered 9.96 million vehicles in 2016, equivalent to one in nine cars sold worldwide. The allegations surrounding Renault follows Volkswagen's emission scandal in 2015, in which the latter admitted to fitting more than 11 million diesel vehicles worldwide with a software that could cheat nitrogen oxide emissions tests.

The German carmaker agreed to pay billions of dollars in federal fines and has pleaded guilty to criminal charges in the US. But Volkswagen has been unable to shake the scandal with German prosecutors raiding the company's headquarters last week as part of an ongoing investigation.