Thousands of Bank of Ireland customers were unable to receive funds last week after an IT glitch caused delays to payment processing.
The system failure meant that public sector workers in Ireland were not paid on Thursday, with chief executive officer Richie Bourcher apologising for the problems, according to the Irish Independent.
"What happened yesterday shouldn't have happened, it was an isolated case but it shouldn't have happened," he said.
"The bank has made heavy investment in IT infrastructure, our systems are robust."
He added: "We are investing heavily and we need to, that is a component of our cost base."
The bank promised in a statement to reimburse customers left out of pocket as a result of the glitch, the origin of which has not been revealed. Some reports suggested that the delays could be related to how Single Euro Payments Area transactions are made around bank holidays.
The IT failure came as Bank of Ireland announced a pre-tax profit of 399 million (£318 million), its first profit since the 2008 financial crisis.
In a separate outage, customers of Natwest were unable to access accounts through mobile devices between 9.55am and 12.30pm on Friday, ahead of planned maintenance over the weekend.
"We're aware of some issues on our Mobile Banking service and are working hard to fix them. Sorry and thanks for your patience," the bank said, before adding that the problems have now been resolved.
Regulators in the UK are currently investigating the ageing legacy IT systems used by banks, following a series of high profile outages. The Prudential Regulation Authority claimed earlier this year that there had been slow progress in making the "antiquated" infrastructure used by banks in the UK and Northern Ireland more robust.