More than 15% of owner-occupier mortgages on Permanent TSB's books have been in arrears for 90 days or more, according to the bank.
This is 1.4% higher than the proportion in arrears at the end of last year.
However, the number of buy-to-let mortgages in arrears has fallen from 21% to 18.8%.
In its results for the first half of the year, Permanent TSB said that, as of 23 August, it had agreed to over 4,000 long-term solutions for mortgage customers who were in arrears.
It said it had also approved €121 million worth of new mortgage lending so far this year.
Between January and June, Permanent TSB made a loss of €131 million, compared to a €587 million loss in the first half of 2012.
However, the group's chief executive, Jeremy Masding ,said the reduction in losses was "flattered by technical accounting issues".
Despite this, he said there had been some improvement in like-for-like operations despite what he described as an "ongoing prudent approach to impairment provisions".
In the first half of the year the bank set aside €430 million for impairment charges and had net exceptional items worth €318 million.
Meanwhile, the bank said it had added almost 30,000 new current account customers this year.
The bank has been offering a fee-free current account in an attempt to attract customers currently with rival providers.