Britain's troubled Barclays bank expressed "deep regret" on Wednesday after it was slapped with a $2.4 billion (2.2 billion euro) fine by US and UK regulators for foreign exchange market manipulation.

Chief executive Antony Jenkins -- who has struggled to restore the bank's damaged reputation following the 2012 Libor interest rate-rigging crisis -- also vowed to continue overhauling the scandal-hit firm.

Six major global banks, including British pair Barclays and Royal Bank of Scotland, were fined nearly $6 billion, mostly for rigging the foreign exchange market, regulators said.

Barclays' fine was the highest because it had not participated in an earlier deal in November between the banks and some of the regulators involved.

State-rescued lender RBS was meanwhile fined another $669 million over the scandal, on top of a £399 million penalty last November.

"The misconduct at the core of these investigations is wholly incompatible with Barclays' purpose and values and we deeply regret that it occurred," Barclays boss Jenkins said in a statement.

"This demonstrates again the importance of our continuing work to build a values-based culture and strengthen our control environment. We remain completely committed to that effort."

Barclays was at the centre of the Libor rate-rigging scandal three years ago when it was fined £290 million by British and US regulators for attempted manipulation of Libor and Euribor interbank rates.

The bank's total forex fine -- equivalent to £1.53 billion -- includes a record £284.4 million to Britain's Financial Conduct Authority for failing to control business practices in its London forex business, while Barclays pleaded guilty to a violation of US anti-trust law.

Barclays was fined $485 million by the New York State Department of Financial Services, $710 million by the US Department of Justice, $400 million by the US Commodity Futures Trading Commission and $342 million by the Federal Reserve.

Barclays also agreed to pay an extra $60 million over its violation of a 2012 settlement for conspiring to rig Libor.

Barclays has also terminated four employees -- three in London and one in New York -- this month and was urged by US regulators to sack four more.

"I share the frustration of shareholders and colleagues that some individuals have once more brought our company and industry into disrepute," added Jenkins.

"Dealing with these issues, including taking the appropriate disciplinary action against the individuals involved, is a necessary and important part of our plan to transform Barclays and remains a key priority."

The group had already set aside £2.050 billion for potential fines arising from the forex affair.
"This is another example of a firm allowing unacceptable practices to flourish on the trading floor," said Georgina Philippou, the FCA’s acting director of enforcement and market oversight.

"Instead of addressing the obvious risks associated with its business Barclays allowed a culture to develop which put the firm's interests ahead of those of its clients and which undermined the reputation and integrity of the UK financial system."

Barclays is continuing to reshape itself under Jenkins, who replaced Bob Diamond as chief executive in the wake of the Libor crisis, but has been plagued by scandals in recent years.

In late Wednesday afternoon deals, Barclays shares rallied 3.16 percent to 271 pence on the London stock market, which was 0.21 percent higher.