German and French officials have discussed plans for a radical overhaul of the European Union that would involve setting up a more integrated and potentially smaller eurozone, EU sources say.

"France and Germany have had intense consultations on this issue over the last months, at all levels," a senior EU official in Brussels told Reuters, speaking on condition of anonymity because of the sensitivity of the discussions.

"We need to move very cautiously, but the truth is that we need to establish exactly the list of those who don't want to be part of the club and those who simply cannot be part," the official said.

French President Nicolas Sarkozy gave some flavor of his thinking during an address to students in the eastern French city of Strasbourg on Tuesday, when he said a two-speed Europe -- the euro zone moving ahead more rapidly than all 27 countries in the EU -- was the only model for the future.

The discussions among senior policymakers in Paris, Berlin and Brussels raised the possibility of one or more countries leaving the euro zone while the remaining core pushes on toward deeper economic integration, including on tax and fiscal policy.

The change has been discussed on an "intellectual" level but had not moved to operational or technical discussions, the EU official said. A French finance ministry spokesman denied there was any project in the works to reduce the currency bloc's membership .

"There have been no conversations between French and German authorities at any level on decreasing the size of the euro zone," the spokesman said .

A radical overhaul of the European Union would be opposed by many members, Reuters reports.