Borse Dubai has reignited last month's controversy over its stakebuilding in Nordic exchange group OMX by challenging the Swedish regulator's verdict that it broke takeover laws, despite escaping punishment for the breach.

The Dubai exchange group, which is vying with US rival Nasdaq in the $4bn (€2.9bn) battle for control of OMX, said in a statement today it has filed an appeal with the Swedish Financial Services Authority. The appeal refers to the regulator's ruling that a Borse Dubai press release revealing it was in the process of buying OMX shares constituted a takeover bid.