The French financial regulator has forced Euronext, the pan-European exchange, to admit that it has held merger talks with German rival Deutsche Börse under new "put up or shut up" takeover rules introduced in France last week.

In response to a written warning about the new tougher rules by the Autorité des Marchés Financiers, Jean-François Théodore, chief executive of Euronext and Reto Francioni, chief executive of Deutsche Börse, confirmed the exchanges had been in recent informal business discussions, Bloomberg reports.