Updated

Barclays, one of Britain's largest banks, is vowing to defend itself against U.S. allegations that it manipulated the electricity prices in California and other western states to make money.

Regulators ordered Barclays and four of its traders to pay $453 million in civil penalties for manipulating electricity prices between November 2006 and December 2008. The Federal Energy Regulatory Commission also ordered Barclays to pay $34.9 million, plus interest, for what it described as "unjust profits" to low income energy assistance programs in Arizona, California, Oregon and Washington.

Barclays says it is disappointed by Tuesday's fines. It insists it has cooperated with the inquiry and that its trading was legal.

Traders Wednesday brushed off the allegations. Barclays' share price traded up 0.9 percent at 311 pence.