RBS to be fined by regulator over mortgage advice -sources

* FCA will provide details on Wednesday - sources

* RBS (LSE: RBS.L - news) could be fined about 15 mln stg - source

* Would be a fresh setback for RBS boss McEwan (Adds details)

By Matt Scuffham

LONDON, Aug 26 (Reuters) - Royal Bank of Scotland will be fined by Britain's financial regulator on Wednesday over mortgage advice given to customers, sources familiar with the matter told Reuters on Tuesday.

The Financial Conduct Authority (FCA) is expected to provide further details, including the level of the fine, at 0900 GMT on Wednesday, the sources said.

RBS could face a penalty of about 15 million pounds ($24.82 million), a person familiar with the matter told Reuters.

It would be the latest setback to hit Chief Executive Ross McEwan, whose efforts to turn around the bank -- which made an 8.2 billion pound ($13.6 billion) loss last year -- are being hampered by ongoing investigations into past misconduct.

RBS, which is 81-percent owned by the British government, is among several major banks assisting regulators around the world investigating allegations of collusion and price-rigging in the global currency market.

It has already been fined 390 million pounds for its role in fixing the benchmark London interbank offered rate (Libor) and has set aside 3.2 billion pounds to compensate customers mis-sold loan insurance.

($1 = 0.6040 British Pounds) (Reporting by Matt Scuffham in London and Karen Rebelo in Bangalore; Editing by Laura Noonan and Pravin Char)