The FT said part-nationalised RBS is facing similar penalties to Barclays, which paid 290 million pounds in fines having agreed a collective settlement in June with United States and UK authorities over attempts to manipulate the Libor interbank rate.

Reuters reported on Aug. 24 that RBS was expected to reach a similar agreement within the next two months.

However, a deterioration in the relationship between regulators on either side of the Atlantic could result in RBS settling first with Britain's Financial Services Authority before reaching separate deals in the U.S, the FT reported.

US authorities were accused of attempting to undermine London as a global financial centre during a recent probe into British bank Standard Chartered.

Any delay in reaching settlements with all the regulators would be a blow to RBS. The bank, 82-percent owned by the government, is under pressure to draw a line under the episode with Britain keen to protect the value of its stake by removing uncertainties over the issue.

RBS, which has sacked four staff in relation to the Libor scandal, said on Saturday it could not comment on when a settlement will be reached or what the level of fines will be. The FSA declined to comment.

More than a dozen banks are under investigation by regulators in the United States, Europe and Asia for suspected rigging of London interbank offered rate, or Libor, and other similar rates which are used to price trillions of dollars worth of financial products.

RBS's Chief Executive Stephen Hester said in August that the bank was ready to "stand up and take any punishment" that comes its way over the issue. Reuters reported in July that RBS and Switzerland's UBS were two of the banks that had played a central role in the manipulation of rates.

Shares in RBS closed on Friday at 235.9 pence. The UK taxpayer is sitting of a loss of nearly 24 billion pounds after bailing the bank out at a cost of 45 billion pounds in 2008.