Ulster Bank Chief Executive Jim Brown has apologised to all the bank's customers and others affected by the bank's IT crash.
In his first interview since the issue began just over one week ago, Mr Brown said that the problem was more complex than originally thought.
He said his focus since then has been on mitigating the effects on customers.
Mr Brown said the backlog should be cleared by early next week and said the bank is making progress.
Asked why there was not a sufficient contingency plan in place to ensure the bank's systems did not fail, Mr Brown said that was something they would look at, but for now their focus was on getting the bank back to normal.
He said its systems are based in Edinburgh and the glitch was caused by an update applied to their batch processing on Tuesday night of last week which caused the problems to its transactions processing.
Asked if there would be any resignations, he said he had no idea.
