The three are Richard Usher, Rohan Ramchandani and Chris Ashton,

They worked at, respectively, the banks JP Morgan, Citigroup and Barclays.

The charges are a follow-up after those banks, along with RBS, paid $2.5bn in fines in May 2015, after pleading guilty to conspiring to rig foreign exchange rates.

In a statement the US Department of Justice said the three men were charged over their "alleged roles in a conspiracy to manipulate" the price of US dollars and euros in the foreign currency exchange spot market.
'The Cartel'

"We previously secured criminal convictions of the financial institutions involved in the misconduct," said Principal Deputy Associate Attorney General Bill Baer.

"Today we seek to hold accountable the individuals who conspired on their behalf."

According to the indictment, between December 2007 and January 2013 a group of traders known as "the Cartel" or "the Mafia" including Mr Usher, Mr Ramchandani and Mr Ashton, "conspired to fix prices and rig bids for the euro-US dollar currency pair".

The DoJ statement also said the former bank traders were alleged to have "gained an unfair advantage on their counterparts by committing corporate fraud involving the manipulation of the foreign currency exchange".

Deputy Attorney General Sally Yates said: "Whether a crime is committed on the street corner or in the corner office, no one gets a free pass simply because they were working for a corporation when they broke the law."

"Today's indictment reiterates our commitment to holding individuals accountable for corporate misconduct," she added.
'Insufficient evidence'

In March 2016 the UK's Serious Fraud Office (SFO) closed its criminal investigation into allegations of price-rigging in the foreign exchange market.

It was set up in 2014 to look into allegations of "fraudulent conduct".

The SFO said it had concluded "based on the information and material we have obtained, that there is insufficient evidence for a realistic prospect of conviction".

At the time it said it would continue to liaise with the Department of Justice over its investigation.
Manipulation

The May 2015 fines paid by the banks were part of a second wave of regulatory sanctions against big international banks for rigging forex rates, almost every day, between 2007 and 2012.

Earlier, in November 2014, six banks were collectively fined £2.6bn by UK and US regulators over attempts by some of their traders to manipulate foreign exchange rates.

In that case, the rate-rigging which the authorities uncovered had been going on since 2008.