RBS has made a loss of £968m in the first quarter of 2016 after a £1.2bn dividend payment to the government.
If the £1.2bn figure is removed then RBS made a pre-tax profit of £421m, up from £37m in Q1 2015.
The bank also announced it was delaying plans to sell Williams & Glyn.
The results say: “Since the last update provided with the 2015 Annual Results, we have undertaken further extensive analysis on the separation and divestment of Williams & Glyn.
“As a result of this analysis, we have concluded that there is a significant risk that the separation and divestment to which we are committed will not be achieved by 31 December 2017.”
RBS says that building a separate IT platform for the sell-off is “challenging” and it is trying to find other ways to separate and sell Williams & Glyn.
The bank adds: “The overall financial impact on RBS is now likely to be significantly greater than previously estimated.”
RBS says its personal and consumer banking lending grew by 15 per cent in Q1, “with strong growth in both the mortgage and commercial businesses.”