The Royal Bank of Scotland's chairman Philip Hampton revealed the bank has suspended bonuses for 50 of its staff after the lender was fined $344m by the UK's regulator and $290m by US authorities for currency market manipulation.
Hampton said in a statement to reporters: "I think it's regrettable. Two clients did express some concerns and, with hindsight, I don't think we followed them up terribly fully."
He added that RBS has already spent "well into tens of millions of pounds on its own FX probe".
The Financial Conduct Authority (FCA) and the US Commodity Futures Trading Commission (CFTC) have fined five banks over $3.4bn collectively for manipulation of the foreign exchange market.
The FCA announced that it has fined Citibank $359m (£225.6m, €288m), HSBC $343m, JPMorgan $352m, the Royal Bank of Scotland (RBS) $344m and UBS $371m.
Meanwhile, the CFTC collectively fined the following banks in civil monetary penalties, specifically: $310m each for Citibank and JPMorgan, $290m each for RBS and UBS, and $275m for HSBC.