"Our partnership is of existential importance for both our countries, which is why open communication, honest exchange and critical debate between us are so important," said German Foreign Minister Johann Wadephul said in a statement sent to AFP.

"Together, we are also aware of our responsibility for Europe. It is crucial for the European Union that France and Germany continue to join forces."

Traditionally the motor of European cooperation, the Franco-German axis has been under some strain in areas from trade to defence to industrial policy.

Wadephul has accused Paris of not always putting its money where its mouth is when it comes to defence spending, and Chancellor Friedrich Merz on Wednesday signalled that Berlin could abandon a joint fighter jet project after quarrels between the contractors.

Paris also opposed a European Union trade deal signed with South America's Mercosur bloc, an agreement strongly backed by Berlin.

And the EU last December also watered down its planned 2035 ban on petrol cars, in large part on German initiative and in the face of French opposition.

Wadephul stressed that "it is crucial for the European Union that France and Germany continue to join forces, that we always seek common ground despite sometimes differing viewpoints".

"Even if there are differences, such as on the Mercosur agreement, there is by far greater agreement on key issues concerning our common European future," he added.

Tensions in the relationship come at a time European leaders have vowed unity in the face of growing discord with the United States on issues from trade to NATO spending and suggestions that the US could annex the autonomous Danish territory of Greenland.