Ulster Bank has said it cannot quantify the proportion of its customers' salary and mortgage payments that have been processed.

IT problems have continued for a tenth day at Ulster Bank, Ireland's third largest retail bank.

Today the bank says that "the bulk" of salary payments are up-to-date, but that some customers might still experience a delay in receiving their pay.

A resolution to the problems is now expected by the middle of next week.

The bank says its call centre has handled approximately 70,000 calls to date this week.

This follows criticism from the Central Bank last night which said in a statement that continuing delays in resolving the failures of Ulster Bank's payment system are "unacceptable".

The bank says 60 of its branches will stay open this Saturday, 22 on Sunday, and 80 branches have extended opening hours.

Royal Bank of Scotland, which owns Ulster Bank, has confirmed that its chief executive Stephen Hester will waive his bonus this year following the computer systems failure which caused disruption to millions of its customers.

"I think it's inappropriate for me to have a bonus this year. We have let our customers down," Mr Hester said.

''That may have arisen from old systems and things that were before my time but I think we could reasonably be expected to have improved things since then and clearly we didn't improve them enough, so it wouldn't cross my mind to have a bonus this year," he added.

RBS is expected to face a bill of £100m sterling or more as a result of the problem.

In January, Mr Hester opted to waive his 2011 bonus, which would have been worth almost £1m.