PARIS (Reuter) - The French Prime Minister, Edouard Balladur, has called for a three-tier Europe in which the strongest states would form the hard core. In an interview released yesterday he described three concentric circles - the inner one grouping some EU countries around France and Germany. 'A smaller number of EU members states must build an organisation better structured, monetarily as well as militarily,' he said of the inner circle. The middle circle would hold the weaker states. The outer would group the rest.