To cancel one high-level Franco-German meeting is unfortunate. To cancel two in less than a week implies a bank of freezing fog is descending over the Rhine.

French and German officials sought yesterday to play down the significance of the abrupt postponement – both by Paris – of two meetings between the countries' most senior politicians.

Privately, and not so privately, the talk in both capitals is of a serious rift in the single most important national partnership in Europe. Officials blame an increasingly difficult relationship between President Nicolas Sarkozy and Chancellor Angela Merkel.

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With France scheduled to take the presidency of the European Union in July, the Franco-German tiff could not be timed worse.

Berlin has been especially annoyed by M. Sarkozy's determination to push ahead with a so-called "Club Med" or formal union of countries on the shores of the Mediterranean. Chancellor Merkel believes that such an organisation would be either a pointless distraction or a threat to the unity of the EU.

There have also been tensions over the management of the euro and on foreign and defence policy. France has repeatedly criticised the monetary policy of the European Central Bank while ignoring its European commitments to restrain its budget deficit. Germany has refused to join a French-sponsored EU military mission to Darfur.

At the heart of the quarrel – not yet an overt crisis – is the strained relationship between the two leaders.

German officials say that the hyperactive and boastful behaviour of the French President – and his over-familiar personal style – has irritated Ms Merkel. French officials suggest M. Sarkozy finds Ms Merkel too cautious and too ponderous. French diplomats also complain that M. Sarkozy – in his determination to shake up all aspects of French government – wants to play down the Paris-Berlin relationship that has been the bedrock of France's domestic and European policy for half a century. "For Sarkozy, the West very much means UK and the US," one French source said.

Late last week, Paris postponed for three months a Franco-German summit that had been scheduled for next Monday in Bavaria. The Elysée Palace said that President Sarkozy's diary was too busy.

Early this week, France called off at, one day's notice, a meeting between the French Finance minister, Christine Lagarde, and her German counterpart, Peer Steinbrück.

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The reason given was trivial, bordering on the insulting. Mme Lagarde had to accompany M. Sarkozy on a visit to a provincial health centre and luxury goods factory.

Eckart von Klaeden, chief parliamentary spokesman for Ms Merkel's ruling conservatives, said the French explanation was " hardly convincing". Martin Schulz, the German Social Democrat leader in the European parliament, said: "I think that Sarkozy has hit such a low that his internal political weaknesses are now beginning to affect Franco-German co-operation."

The newspaper Le Monde said that, whatever excuses were put forward, it was clear that Franco-German relations had fallen victim to a "maladie diplomatique".

Le Monde said that you had to go back eight years, to a spat over EU voting rights between Chancellor Gerhard Schröder and President Jacques Chirac, to find such a "sullen" relationship between the "countries which once claimed to be the motors of Europe". M. Sarkozy wants to make his plans for a Mediterranean Union one of the centrepieces of his six- month presidency of the EU from 1 July. He has invited the Mediterranean states to a summit in Paris on 13 July and wants other EU countries to come along the next day – France's national day – to bestow their blessings.

However, several northern EU countries, led by Germany, are deeply unhappy about the French initiative. They complain that there is no need for a separate Mediterranean Union, distinct from the EU's own partnership agreements with its southern and eastern neighbours.

The German newspaper Die Welt said M. Sarkozy had tried to persuade Ms Merkel to write a joint article, praising the Club Med idea, for publication in French and German newspapers before next week's bilateral summit. She refused. M. Sarkozy then postponed the meeting.

The French and German governments insisted officially that the postponement was a timetabling problem.