Britain's financial watchdog said Monday it had fined Merrill Lynch International a little over £34.5 million ($45.4 million, 38.6 million euros) for failing to report tens of millions of trades.

The Financial Conduct Authority said in a statement that the fine relates to 68.5 million unreported transactions over two years to February 2016 -- and follows previous warnings and fines for similar offenses.

The FCA added that this time around, it was "the first enforcement action against a firm for failing to report details of trading in exchange traded derivatives, under the European Markets Infrastructure Regulation (EMIR)" that was introduced following the global financial crisis to provide greater transparency on deals.

Merrill Lynch International, part of U.S. giant Bank of America Merrill Lynch, would have been required to pay £49.32 million had it not settled at an early stage of the investigation, the FCA said.

"Reporting exchange traded derivative transactions helps authorities assess and address the risk inherent in financial systems caused by a lack of transparency," the watchdog said.

"The reporting requirement was one of the key reforms introduced following the financial crisis in 2008 to improve transparency within financial markets."

Bank of America Merrill Lynch said in a separate statement that it had self-reported the issue to the UK watchdog, insisting that none of its clients had been financially impacted.