OMX said shareholders that entered into options agreements with Borse Dubai did not receive better conditions as the Dubai exchange group challenges the Swedish regulator's verdict that it broke takeover laws in its battle for the Nordic exchange company.

Nasdaq struck a deal in May to take over OMX for $3.7bn (€2.7bn) in cash and shares, but has since seen that deal trumped by a $4bn cash bid from a Dubai rival.