Mercedes-Benz says several hundred of its vehicles remain blocked from delivery to France as the dispute surrounding the manufacturer's air-conditioning refrigerant preference shows no sign of being resolved.

The argument centres on Mercedes' use of the r134a refrigerant - first introduced as a replacement for R12 freon in the early 1990s - as opposed to the 1234yf variant believed to be lower in CO2 emissions - but which the German manufacturer strongly contends can ignite in certain conditions.

The row has reached the top echelons of political power with European Commissioner, Antonio Tajani, appearing to take Paris' side and the German Ministry of Transport also involved in discussions to unblock the freezing of Mercedes' A, B and CLA model deliveries.

"It is several hundreds of cars that our customers are waiting for," a Mercedes spokesman told just-auto from Germany.

"We do not have any statement from the French authorities why they block the registration of our vehicles - there are still discussions going on between the EC and the German Ministry of Transport."

Despite what appears to be significant opposition to Mercedes' use of the r143a refrigerant, the automaker nonetheless received some highly unusual backing last week from environmental lobby group, Greenpeace, which is firmly opposed to the alternative r1234yf.

"The new chemical does indeed contribute less to global warming, but the real impacts of the new generation of CFCs are completely unpredictable," said Greenpeace special projects campaigner, Wolfgang Lohbeck. "Of course it is unfortunate this means a a longer transition period for r134a.

"But compared to the establishment of yet another CFC as a successor refrigerant, it is the lesser evil."

The r1234yf refrigerant is currently being tested by the German road safety authority, the Kraftfahrt-Bundesamt (KBA), which, although not responsible for testing chemicals, is tasked with certifying car safety.

"There are on-going tests at the KBA and what they told us [is] they will need another couple of weeks to finalise their report," said the Mercedes spokesman.

"The tests are strictly confidential and we have no indication yet."

Mercedes insists its refrigerant complies with the European Union Directive on Mobile Air Conditioning (MAC), although Tajani recently noted: "Article 29 of the framework directive provides for the possibility for member states to adopt temporary safeguard measures, if some conditions are met and a specific procedure is followed.

"If this procedure is triggered, the commission may consider the French initiative within this framework."

No-one from France's Ministry of Transport under whose auspices the certification authority, the Systeme d'Immatriculation des Vehicules (SIV), operates, was immediately available for comment from Paris.