The Central Bank said it is "concerned by the unacceptable delays" in resolving technical issues which have caused a huge backlog of transactions at Ulster Bank.
In a statement issued last night the Central Bank said it has been in daily contact with Ulster Bank since the problem came to light last week, and it is concerned about the impact the delay in fixing the fault is having on customers.
"The Central Bank of Ireland is concerned by the unacceptable continuing delays by Ulster Bank in fully resolving the failure of its payment system and the consequent impact on its customers," the statement said.
"The Central Bank is working with the UK Financial Services Authority and the Bank of England in investigating the root cause of the issue at the Group level and how this has impacted Ulster Bank’s payment systems."
Meanwhile, the chief executive of the Ulster Bank group is insisting that customers are sticking with the bank in spite of the software problem.
Jim Brown also says the backlog should be cleared by early next week.