National Australia Bank said the scale of losses it had incurred as a result of a foreign exchange trading scandal was 185 million Australian dollars (€116 million) compared with its original estimate of Aus$180 million.

In a statement yesterday, NAB's chief executive, Mr Frank Cicutto, said its internal investigations into unauthorised foreign currency options trading had progressed.

In view of the unauthorised activity that has occurred in this portfolio, he said NAB was undertaking a market revaluation of the remaining portfolio to ensure it conformed with its policies.

"Our initial view indicates that this revaluation will lead to additional losses. Based on our work to date, there is a very low probability that the total losses will be as high as market speculation of $600 million. We expect to provide a further update on this matter by the end of the week."

NAB chairman Mr Charles Allen said: "Following the outcomes of the investigations, we will take whatever action is necessary to ensure that investors, customers and staff have full confidence in the National."

NAB owns National Irish Bank and Northern Bank and employs more than 2,000 staff in Ireland. It has said that its Irish operations are unaffected by the fraud.