Ulster Bank has announced a loss of £761m (€887m) in 2010, according to figures from its parent bank Royal Bank of Scotland.
The figure, which is almost double the £368m (€433m) recorded in 2009, included almost £1.2bn (€1.4bn) which was set aside for loan losses, up from £649m (€764m) in 2009.
Excluding loan losses, profits were up 50% to £400m (€471m), mainly due to cost cuts.
RBS said the increase in loan losses at Ulster Bank reflected the "deteriorating economic environment" in Ireland and rising default levels in personal and business loans.
RBS said: "Higher unemployment, lower incomes and increased taxation have led to increases in mortgage loan losses."
Ulster Bank has also transferred some of its bad assets to a section of RBS. Impairment losses on these were just over £2.7bn (€3.1bn) last year, up from £1.4bn (€1.6bn) in 2009.
Loans to customers fell by 5%, with the bank describing levels of new business as "muted".
The bank said customer deposits had remained stable in the final three months of last year, and were up 8% over the whole of last year.