French carmaker Renault on Monday promised to come up with a "technical plan" over coming weeks to bring down harmful emissions of its vehicles.

On Thursday, a government-appointed commission said that Renault's diesel cars failed pollution tests and investigators raided its facilities, raising fears the French carmaker could be caught up in an emissions scandal similar to the one engulfing Volkswagen, which has admitted to using cheating software to fool tests.

France's Environment Minister Segolene Royal made the announcement after the commission submitted test results of French and foreign vehicles, which found carbon dioxide and nitrogen dioxide emissions in Renault cars to be too high, as were those of several non-French.

"We are working on a technical plan which should allow us to cut emissions," Renault sales director Thierry Koskas said during a presentation on the group's 2015 sales performance.

Unit sales grew 3.3 percent from 2014 to 2.8 million units worldwide.

"Renault did not cheat," Koskas said, referring to questions raised last week over how emissions levels could be so different between test conditions and real conditions on the road.

"In test conditions, we respect emissions norms," he said.

He gave no details of what the "technical plan" may entail.

Shares in Renault and other car companies skidded last week amid fears that the emissions scandal engulfing Volkswagen may be spreading sector-wide.

Renault stocks slumped by more than 20 percent during Thursday's session after unions reported that anti-fraud investigators had raided several of the company's sites, possibly looking for emissions cheating software on diesel engines, before closing around 10 percent lower. On Friday, they lost another 3.4 percent.

In early trading on Monday, the stock was down again, by 2.2 percent at 73.51 euros, taking the decline over three days in the group's market capitalisation, its stock exchange value, to around 3 billion euros ($3.3 billion).