The director of consumer protection at the Central Bank has said he expects Ulster Bank to stick to commitments to resolve its technical problems by the end of the week.
Bernard Sheridan said the Central Bank had been dealing with Ulster Bank at the highest level.
He said the bank had improved its communication with customers in recent days but that communication had been lacking last week.
It is now almost a week since a ''technical glitch'' at Ulster Bank resulted in missed payments and direct debits affecting over 100,000 people.
On Friday, the bank said it aimed to resolve the problem by the time normal business resumed this morning.
But last night Ulster Bank conceded this was impossible and said it could take until the end of the week for all the problems to be addressed.
Bernard Sheridan, director of consumer protection at the Central Bank, said that Ulster Bank had promised to fix the problem by the weekend and that he expected them to fulfil that promise.
He was also critical of Ulster Bank's communications with customers and the public on the matter, saying it had improved over recent days but that it could have been better at an earlier stage.
Meanwhile, 80 Ulster Bank branches extended their opening hours today as the bank continued to attempt to clear the backlog in payments caused by its IT failure. The bank said the scale of the backlog is ''unprecedented''.
A statement on the Ulster Bank website this evening said that branches will continue with extended hours for the rest of the week with most branches opening from 9.30am until 7pm.
Payments from Ulster Bank into other banks are said to be nearly cleared but a major issue remains with updating the bank's own accounts, processing incoming payments and updating balances.
The bank has been facilitating customers who call into branches with payslips and giving them cash. But this week presents a challenge as many monthly salaries will have to be processed. Social welfare payments going into Ulster Bank accounts may also be hit.
Meanwhile, The Central Bank said it had been in contact with Ulster Bank at the highest level to press the bank to resolve the situation as quickly as possible and ensure that customers are treated fairly.
''The Central Bank's concern is to ensure that all customers are supported and accommodated by Ulster Bank until the system is fully operational again and we have made this clear to Ulster Bank,'' a statement from the Central Bank said.
It said that it emphasised the importance of clear communication and support to consumers at a meeting with senior management of Ulster Bank earlier today.
The Central Bank said that Ulster Bank had committed to ensuring that no customer will be at a financial loss and to providing up-to-date and clear information to customers.
RBS could face £100m sterling bill or more after IT failure
Royal Bank of Scotland, which owns Ulster Bank, was expected to face a bill of £100m sterling or more from the computer systems failure that caused massive disruption for millions of customers in Ireland and the UK.
RBS said it will operate extended hours at 1,200 of its NatWest branches in the UK for the rest of the week. Ulster Bank branches will also extend their opening hours for the rest of the week.
The banks also opened for business for the first time on a Sunday yesterday as staff struggled to help customers. One banking industry source estimated the cost of the glitch would cost between £100-200m sterling.
RBS must pay the extra costs of opening the branches for longer and drafting in staff over the weekend, as well as compensating customers for difficulties arising from missed payments.
In a message posted on the RBS website, chief executive Stephen Hester said customers should approach the bank directly to seek compensation.
The episode is a further embarrassment for Hester, who admitted in February he had considered resigning following a public outcry over a proposed £1m bonus payment which he opted to waive following pressure from politicians.
