Chief Executive Officer Ross McEwan would not comment on the investigation directly, but said the bank would "come down very severely on anyone ... breaking the rules," The Daily Telegraph reported Saturday.
McEwan's comment came as British bank Barclays became the latest financial giant to suspend staff implicated by the investigation into manipulation of the $4.7 trillion global currency markets.
Barclays has suspended six traders. RBS has reportedly suspended two traders and Citigroup has suspended one, the newspaper said.
Given the size of the market only a small tweak in exchange rates can affect huge amounts of money.
The newspaper said the investigation is looking into collusion among traders who exchange information online in chat rooms.
In the chat rooms, traders identify themselves with pseudonyms such as "The Bandits Club," "The Cartel," and "The Dream Team," the newspaper reported.