National Australia Bank (NAB) said losses run up by the four staff it suspended last week for rogue trading could go as high as A$600m ($455m).

It initially estimated the losses at A$180m but has now added a further A$5m to its known losses.

The rogue trades are being investigated by Australian police and financial regulators as well as an NAB inquiry.

Losses set to rise

NAB chief executive Frank Cicutto said the bank was carrying out a revaluation of its foreign exchange options trading.

"Our initial view indicated that this revaluation will lead to additional losses," Mr Cicutto said.

"There is a low probability that the total losses will be as high as market speculation of A$600m," he added.

NAB has appointed auditors Pricewaterhouse Coopers to get to the bottom of the scandal; that inquiry is due to report before the end of February.

NAB has suspended four traders in its Melbourne office and one of its London staff.

NAB owns just over 5% of troubled Australian insurance business AMP and has tipped in the past as a potential buyer for the rest of the business, which owns Pearl, NPI and London Life in the UK.

If NAB's losses from the rogue trading scandal do approach A$600m that would represent a hefty blow to the bank, which posted 2002 net profits of A$3.9bn.