Barclays and four of its power traders have been ordered to pay a total of $453 million by the US energy regulator for allegedly rigging US energy markets. This comes at a time when the bank has been looking to recover from last year's Libor-rigging scandal.

The Federal Energy Regulatory Commission said the bank must pay $435 million within 30 days for manipulating electric energy prices in California and other western markets between November 2006 and December 2008. The individual traders must pay the remaining amount out of the total of $453 million.

Barclays denied the allegations and said it intended to "vigorously defend this matter".

The fine was originally proposed in October last year and upheld following a review by the regulator.

The case now looks likely to go before a US federal court.

"We believe the penalty assessed by the FERC is without basis, and we strongly disagree with the allegations made by FERC against Barclays and its former traders. We believe that our trading was legitimate and in compliance with applicable law," Barclays said in a statement.

FERC used emails between the traders detailing how they allegedly manipulated electricity trading to help build the case against Barclays.

Ex-managing director of the banking team, Scott Connelly, must pay $15 million, whilst the three former Barclays traders, Daniel Brin, Karen Levine and Ryan Smith, were ordered to pay $1 million each.

The bank will also have to forgo $34.9 million in profits, which will be distributed to low-income energy programmes in Arizona, California, Oregon, and Washington.

The penalty comes on top of what has been a difficult period for the bank.

Last year, Barclays was fined £290 million ($441.5 million) by UK and US regulators for attempting to rig the key LIBOR interest rate.

The bank has also had to set aside £2.6 billion to cover compensation claims for the payment protection insurance scandal and another £850 million to cover the mis-selling of interest rate hedging products sold to small firms.