Paris (AFP) - The relationship between French President Emmanuel Macron and German Chancellor Angela Merkel, long seen as Europe's defining political alliance, is undergoing a period of unprecedented strain as reality clashes with expectation.

At a news conference on Thursday night, Macron unexpectedly laid bare the extent of his disappointment with Berlin by bluntly reeling off a string of areas where he disagrees with Merkel.

And analysts say that with European elections looming at the end of next month -- and the conservative Merkel and centrist Macron each having different political priorities -- the strains risk intensifying further.

"Emmanuel Macron is no longer hiding his impatience towards Germany," said Claire Demesmay, head of the Franco-German relations programme at the German Council on Foreign Relations.

"We have clearly moved into an electoral cycle and one of political competition. The two leaders follow two antagonistic logics. And they need to show this to public opinion," she told AFP.

During his address, Macron listed some of the issues causing tension with Merkel:

Brexit -- While Merkel favoured granting London a long extension for Britain's departure from the EU, Macron argued for a short one, but in a classic EU compromise, the date was set as October 31.

Trade -- Macron referred to what he described as the "incoherent" decision backed by Berlin to begin EU trade talks with the United States.

Climate -- France was particularly piqued that Germany wanted trade talks with the United States without Washington being a party to the Paris climate accord to cap global emissions, which Trump dumped in 2017.

Economic policy -- Macron said Germany was "at the end" of a growth model that had seen it profit from "imbalances" within Europe and in low-wage countries "which is contrary to my social project".

Stressing that the national interest can sometimes trump European interests, he said a culture of compromise should not stop France from "affirming a French position when there is one".

"There is a sense of disappointment vis-a-vis Germany," said a French diplomatic source, asking not to be named.

'German taboos'

The relationship between France -- militarily defeated by the Third Reich in the early phase of World War II -- and postwar Germany has defined modern European history.

German chancellors and French presidents have for the last decades formed a succession of power couples that analysts have defined as the Franco-German motor of Europe.

These have included the historically-symbolic relationship between postwar leaders Charles de Gaulle and Konrad Adenauer, followed by Georges Pompidou and Willy Brandt.

Then came the extraordinarily tight tandem between Francois Mitterrand and Helmut Kohl, which oversaw the fall of communism in a relationship symbolised by an image of them holding hands at a World War I battlefield.

Most recently, the relationship between Merkel and Nicolas Sarkozy became so politically intimate they were dubbed "Merkozy" by the press.

Macron, who has always presented himself as a statesman of international stature, has never made a secret that his vision of liberal reforms for France should be spread across Europe.

But despite the signing in January 2019 of a new Franco-German Treaty on cooperation and integration, Macron was possibly asking too much to expect Berlin's unconditional support.

Macron had been thwarted by "the taboos of German political culture" on issues of financial solidarity in Europe, said Remi Bourgeot, a specialist on Germany at the Institute of International and Strategic Relations in Paris.

"This is all in contradiction with the German position" and its "model of cost-cutting", he said.

'Normal and necessary'

But on Thursday, Macron also said disagreements were healthy in any relationship, adding that Franco-German dialogue required "sometimes accepting fruitful confrontations but always with the desire to ultimately find a compromise."

In Berlin, deputy government spokeswoman Ulrike Demmer played down the idea of a major squabble, saying there were "occasional differences of opinion" but these were "normal and necessary".

With Merkel now in power for 13 years, there is also certain to be a change at the top in Berlin after her vow to step down in the 2021 polls. Macron will also face re-election in 2022.

Even on the day of Macron's address, Berlin and Paris again showed their ability to form a foreign policy tandem by condemning Moscow in a joint statement for easing Russian citizenship rules in separatist-held areas of east Ukraine.