The French president sided with federalist Euro-MPs who are engaged in a bitter feud with Vaclav Klaus, the Czech president and a Eurosceptic.
Senior MEPs, including the president of the European Parliament, Hans Gert Poettering, caused a diplomatic incident ten days ago after demanding that Mr Klaus hoist the European flag over his residence during bad tempered talks in Prague.
“It was a wound, it was an outrage to see that flags had been taken down from public buildings,” said President Sarkozy, the current holder of the EU’s six-month rotating presidency which he hands over to the Czech Republic in January.
“Mr Poettering can count on the full support of the French president.”
Karel Schwarzenberg, the Czech foreign minister, hit back as the diplomatic war of words between Paris and Prague threatened to overshadow the smooth transfer of the EU presidency.
“There is no law binding the Czech Republic to hang the EU flag over Prague Castle. Prague Castle is a symbol of the Czech state and not the EU,” he said.
“It is not up to the head of another state to criticise the Czech president over flags.”
A statement from the office of Mr Klaus said: “The Castle is a symbol of Czech statehood. There is no reason to change this historic tradition.”
The row exploded when a delegation of Euro-MPs sarcastically presented Mr Klaus with the 12-starred flag, during a visit on Dec 5, knowing that he had ruled out flying the flag over Prague Castle.
He was especially angered when Dany Cohn-Bendit, a former 1968 student radical and the Franco-German leader of Green Euro-MPs, told him: “I don’t care about your opinions”.
Mr Klaus replied: “This is incredible. I have never experienced anything like this before.”
Nigel Farage, the leader of UK Independence Party, compared the EU flag demand to the behaviour of Nazi or Soviet officials, both dictatorships that had occupied Prague and its Castle in the past.
“The manner in which Cohn-Bendit demanded that President Klaus fly the EU flag over his castle could easily have been done by a German official of over 70 years ago or a Soviet official of 20 years ago,” he said.
“No doubt they think that Buckingham Palace should fly the EU flag to show its dominium.”