EU anti-trust regulators have started an investigation into the proposed merger of Deutsche Börse and NYSE Euronext, citing concerns about the impact on derivatives and equities trading. EU competition commissioner Joaquin Almunia had flagged the move several times in the past couple of months. The investigation follows a month-long preliminary review which ended yesterday.

Regulatory approval in Europe and the United States is the last part of the process before the companies can merge to become the world largest exchange operator.