Deutsche Börse, the German stock exchange operator, defended criticism that it overpaid with its $2.8bn (€2bn) bid for the International Securities Exchange that will allow it to triple its presence in the US options market.

The merger between Deutsche Börse's Eurex and ISE still requires regulatory approval from the US Securities and Exchange Commission, anti-trust authorities and ISE shareholder approval but the the exchanges expect the deal to close by the end of the year. The agreement includes an $85m breakup fee if ISE backs out of the deal.