France has blocked the registration of some new Daimler Mercedes cars in an escalating row over the German company’s use of a banned air conditioning coolant, EU sources say.

French authorities have refused to register Mercedes A-Class, B-Class and SL cars assembled since 12 June, even though German authorities have approved them, a Daimler spokesman said.

Usually, French approval automatically follows a German green light. But "We have no explanation for why the registration in France was not yet accepted," the spokesman said.

An informed EU official said that Paris had blocked the registration because the cars contained a coolant which is not permitted in the EU.

The source added that the French transport ministry had informed the Commission about their plans this week and that the Commission would discuss the matter at their next automotive meeting in mid-July. French government officials have not commented.

In September, Daimler said that HFO-1234yf, the only air conditioning coolant on the market that conforms to a new EU directive on greenhouse gases, could be the primary source for a vehicle fire.

Daimler and its rival Volkswagen are both developing expensive carbon dioxide-based air conditioning systems in order to avoid what they say is a fire hazard posed by Honeywell and DuPont's new refrigerant HFO-1234yf, which emits poisonous hydrogen fluoride gas when it burns.

Meanwhile, Daimler is violating the EU directive by continuing exclusively to use the highly polluting coolant chemical R134a. The German authorities agreed to extend a permit previously granted to Daimler’s cars to its new models.

General Motor's European unit, Opel, began installing HFO-1234yf-based systems in its Mokka model at the start of the year.

Opel said it had found no evidence in a crash test on its new Mokka SUV that the air conditioning refrigerant could catch fire in a collision and release toxic fumes.