BBC News reports that a ruling on the involvement of RBS in the fixing of the key industry interest rate is due imminently.
It is expected to be higher than the fine of nearly £300m imposed on Barclays last year.
RBS, which is majority owned by the government, is now in final talks with US and UK authorities over Libor.
In the meantime, Royal Bank of Scotland will next week agree a settlement with U.S. and British authorities for its part in a global rate rigging scandal, sources familiar with the situation told Reuters.
More than a dozen banks around the world have been scrutinized by regulators as part of an investigation into the suspected rigging of interbank rates, which are used to price trillions of dollars of financial instruments.
image: © Elliott Brown