Ratings agency Fitch Ratings held a 'BBB+' rating on Royal Bank of Scotland amid unexpected revelations it faced a $13bn payout to settle a court case brought by a US government department.Fitch said in a note while the latest round of conduct and litigation fines would immediately impact profit, there was a meaningful cushion to absorb further legal costs in its capital base.A loss this year was expected, the ratings agency said, but added the bank could gradually improve its rating.Strong medium-term challenges included the uncertainty of size and timing of further regulatory fines, Fitch said.Shares in Royal Bank of Scotland fell by 1.56% on Friday at 1624 BST to 360.40p.