The FRC, which has powers to fine and suspend accountants, said in November it was scrutinising financial reports by the bank.
KPMG said it understood the need for appropriate regulatory scrutiny and said it would co-operate fully with the investigation.
In a statement KPMG said: "As auditor to the bank we believe that we have provided, and continue to provide, robust audits which provide rigorous challenge to the judgements and disclosures proposed by the bank's management."
