In a short statement ANZ says it has extended the offer period from 18th April to 4th May, but the bank has not raised its offer.

ANZ offered in February to acquire the 65.8% stake it does not already own in Internet broker E*Trade Australia for around A$268 million.

At the time Kerry Roxburgh, chairman, E*Trade Australia, said the bid was in the "best interests of all shareholders". But last month Roxburgh recommended that shareholders reject the ANZ offer and argued that the recommendation was made in the absence of a superior offer and subject to an independent expert's report.

ANZ's offer values ETrade at A$407 million, but E*Trade Australia said an independent expert's valuation valued the business at between A$424 million to A$476 million.

But, according to Australian press reports, Brian Hartzer, ANZ group managing director, personal division, says in a letter to shareholders that the independent expert's valuation is "unrealistically high" and at a substantial premium to all other listed online brokers in Australia and the US.

Last month Roxburgh also argued that E*Trade Australia shares had consistently traded above A$4.05 since ANZ made its cash offer. But the stock has since fallen from A$4.19 - the average price of the shares when the board changed its mind about the ANZ offer - and closed at A$4.14 on Tuesday.

In a statement Hartzer says E*Trade Australia also faces a number of uncertainties and business challenges which are mentioned in the report.

"Shareholders would benefit from more time to fully consider ANZ's A$4.05 cash offer given the implications these uncertainties and challenges may have for the future value of E*Trade Australia," he says.

ANZ needs 90% acceptance of its offer for E*Trade but has faced shareholder opposition since disclosing details of its bid.

In February boutique fund manager Caledonia Investments has increased its stake in the unit from 9.45% to 10.46%, while Invest4Profit - a share research and advisory firm that claims its members collectively own around 10% of E*Trade Australia - has called for shareholders to reject the ANZ deal.

Furthermore Australian broker IWL said last month it may put forward a rival proposal to ANZ's bid for E*Trade Australia after it acquired a "strategic stake" in the Internet brokerage unit.

But ANZ's 34.2 per cent stake in the business rules out another party taking over the Web broker without its support.