A judicial investigation into diesel emissions testing in France could widen beyond Renault after tests showed other carmakers had exceeded the authorized levels, the French environment minister said on Sunday, without elaborating.

Shares in Renault fell more than 4 percent to their lowest level in around a month on Friday after a source at the Paris prosecutor's office said it had launched a judicial probe into possible cheating on exhaust emissions at the French carmaker.

Volkswagen's admission that some of its diesel vehicles were fitted with software designed to hide the true level of emissions they produced has highlighted that most cars spew out far greater amounts of health-threatening nitrogen oxide in everyday driving conditions than in laboratory tests.

"A number of anomalies were noted on Renault vehicles. The controls performed far exceeded the permissible standards. This is also the case for other carmakers to a different extent. So there could be other investigations," Environment Minister Segolene Royal said in an interview with French weekly Le Journal du Dimanche.

"It is a matter of justice and I do not interfere."

Renault said it respected all laws concerning exhaust emissions, adding that its vehicles did not have software enabling them to cheat on emissions standards.

In addition to Volkswagen, Renault is the only carmaker so far to be referred for possible criminal investigation in France over suspected breaches of emissions rules.

"I have no reason to think Renault cheated like Volkswagen," Royal said.

Volkswagen this week agreed to pay $4.3 billion in a settlement with US regulators.