The European Commission has taken a first step to ensure Germany's giant auto industry switches to a new air conditioning coolant deemed to be more environment friendly, a senior official said on Thursday.

EU rules require use of the new coolant from January this year but Daimler, one of the world's biggest automakers, said it posed safety problems in some of its models and won a six-month reprieve for further testing.

The coolant manufacturers say the tests prove it is safe.

"I have written a letter (to the German government) about the problem before starting a formal breach of rules procedure," EU Industry Commissioner Antonio Tajani said.

"I have committed ... to ensuring the rules are respected and I will keep my word," Tajani said, adding that the letter was meant "to start a dialogue."

"Our objective is to resolve problems but if Germany does not respect the law, then we will be obliged to launch a formal infraction procedure since if we do not, we could be accused of failing to meet our responsibilities."

Aides to the Commissioner said the letter was sent on Monday and gave the German authorities 10 weeks to resolve the problem.

The new air conditioning coolant is said to sharply reduce a car's greenhouse gas emissions, blamed for global warming, and to be much less harmful to the environment.

It was initially tested extensively and approved by the German Automakers Association, VDA, of which Daimler is a member.

Daimler said that when it used it in new models, the coolant proved highly inflammable in certain cases.