The US Federal Reserve has confirmed that it is investigating a number of unnamed banks for improper conduct around the currency markets and is working with the Department of Justice and overseas authorities within its probe.
However, the spokesperson did not name the individual banks.
The announcement comes only a few hours after the Financial Conduct Authority (FCA) and the US Commodity Futures Trading Commission have fined five banks a combined total of $3.4bn (£2.1bn, €2.7bn) for their role in the manipulation of the foreign exchange market.
The authorities announced that they fined Citibank, HSBC, JPM, the Royal Bank of Scotland (RBS) and UBS.
Meanwhile, the FCA said Barclays has not incurred a fine, but remains under investigation over allegations of currency rigging.
The regulator said it will progress its "investigation into Barclays which will cover its G10 spot FX trading business and also wider FX business areas".
The FCA investigation has lasted 13 months and involved over 70 enforcement staff and "unprecedented cooperation with domestic and international regulators".