However, shares in the group were up almost two per cent in early trading.
The bank said this takes the total sum it has provided for such matters to £6.7bn, or $8.3bn. Last year, it emerged that RBS could be facing a fine from the US Department of Justice (DoJ) as high as $12bn.
RBS said it was still cooperating with the DoJ in its civil and criminal investigations of RMBS matters, and the bank said it "considers it appropriate to take this provision now in relation to those investigations as well as other RMBS litigation matters".
"The duration and outcome of these investigations and other RMBS litigation matters remain uncertain, including in respect of whether settlements for all or any of such matters may be reached," the bank said in a statement this morning.
"Putting our legacy litigation issues behind us, including those relating to RMBS, remains a key part of our strategy. It is our priority to seek the best outcome for our shareholders, customers and employees," said RBS chief executive Ross McEwan.
RBS was the worst performer among the UK's largest lenders when the Bank of England conducted stress tests last November. After failing on all the central bank's key measures, the group announced plans to cut costs and sell non-core assets - such as Williams & Glyn, which it has been struggling to offload for some time now.