"The development of the hydrogen market will be delayed if there is no equal treatment between renewable and low-carbon hydrogen," the French ambassador to Germany Francois Delattre said in Berlin.

Low-carbon electricity for hydrogen production included nuclear power, Delattre said at an event to mark German network operator OGE's move to join the H2Med project to bring hydrogen from the Iberian peninsula to the rest of Europe.

Discussions are ongoing between EU member states on a package of regulations that will determine whether volumes of the gas produced with nuclear power can be considered "green".

"Much progress remains to be made on this equal treatment and we must mobilise together in this direction," Delattre said.

Paris has repeatedly clashed with Berlin over nuclear energy playing a bigger role in Europe's energy plans.

While France uses nuclear to generate around 70 percent of its electricity, Germany switched of its last reactors in April even as Berlin seeks to wean Europe's largest economy off fossil fuels.

By the same token, Berlin sees hydrogen as an avenue to reduce use of natural gas and decarbonise its industries.

Germany signed up in January to the H2Med project, the centre of which is a major undersea pipeline connecting the northeastern Spanish port of Barcelona to France's Marseille.

The pipeline is set to be completed by 2030 and have an annual capacity of two million tonnes, estimated at 10 percent of European consumption.

Progress on the project "has not always been easy", Franziska Brantner, state secretary at the German economy ministry, said at the signing event.

Brantner however said she had "great confidence" that work would continue "fast enough".