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.