In a major speech in the port of Toulon, Mr Sarkozy said he and the German Chancellor, Angela Merkel, would meet on Monday to propose measures to "guarantee the future of Europe".

He warned that economic convergence would be long and difficult. But he promised that France would not give up its sovereignty.

He said the euro could not continue to exist unless eurozone economies pulled together.

Europe had to be "refounded" he said, with France and Germany at its heart to ensure "a zone of stability". "We must confront those who doubt the stability of the euro and speculate on its break-up with total solidarity.

"France is fighting so that Europe can still make its voice heard in the world of tomorrow," he said. Stricter financial discipline was needed, he added, with more severe sanctions for countries which did not meet their responsibilities.

Mr Sarkozy also made a robust defence of measures he had already introduced to tackle France's debts. He said the country had to end doubts about its ability to pay, in order to avoid being targeted by speculators.

European Union leaders will hold a summit in Brussels next week, which is seen by many analysts as a crucial moment in efforts to tackle the debt crisis.