Werner Seifert, chief executive of Frankfurt stock market operator Deutsche Börse, has rounded on one of the hedge funds trying to oust him. Just last week Seifert called for a truce.

In an open letter to Christopher Hohn, managing partner of The Children's Investment Fund, Seifert accused the hedge fund of mounting "unfounded attacks" on both him and on Rolf Breuer, chairman of the exchange's supervisory board and damaging the exchange, its owners, customers and employees.