Northern Bank blamed the "fragile" economic environment after losses for the first quarter of 2012 doubled to £54.5m.
While the bank's pre-impairment profits had grown up by over 51% to £18m, the gain was eliminated by impairment charges of £72.5m.
Total income was up 11% to £47.5m and costs were down 4% to £29.5m.
But the loss was double that of the £27m sustained in the same period last year.
The bank said that impairment charges were "elevated given the ongoing condition of the property market, where we have continued to take a very cautious assessment of the valuation of impaired assets".
Chief executive Gerry Mallon said the bank showed a "strong underlying performance" with profits up 51%.
"However, we are not immune to the environment in which we operate. Both national and international market conditions remain challenging and have led to a continued high level of impairment charges.
"Despite the external factors beyond our control, we are in a strong position to meet the challenges ahead and to win new customers from our competitors."
He said that the bank was responding to changing consumer habits and was pleased to have recently registered its 100,000th customer for online banking.
However, it has also closed a large number of branches with another four branches due to shut by the middle of June, leaving it with around 70.
Mr Mallon said that the branch closures were "difficult decisions" and that the hard times were not over yet.
"There is no doubt that 2012 will be a tough year for Northern Ireland, with continued low economic growth, low interest rates and a sluggish property market all leading to elevated impairment charges," he said.
"However, as a bank with a very high level of capital and liquidity, a strong parent and still 100% shareholder owned, we are well placed to comfortably withstand the economic conditions.
"Our clear direction, competitive products and services and appetite for growth mean we are also well equipped to strengthen our market position further."
Meanwhile, Danske Bank Group announced pre-tax profits of £177m, with impairment charges climbing to £440m from £337m in the first quarter of 2011.