'Plausible allegations that a conspiracy existed': Barclays, RBS, and 5 other top banks settled a US rate-rigging lawsuit for $324 million

NEW YORK (Reuters) - Seven of the world's biggest banks have agreed to pay $324 million (£222.7 million) to settle a private US lawsuit accusing them of rigging an interest rate benchmark used in the $553 trillion (£380.2 trillion) derivatives market.

The settlement made public on Tuesday resolves antitrust and other claims against Bank of America, Barclays, Citigroup, Credit Suisse, Deutsche Bank, JPMorgan Chase & Co and Royal Bank of Scotland Group.

Several pension funds and municipalities accused the banks of engaging in a conspiracy to rig the "ISDAfix" benchmark from 2009 to 2012.

The ISDAfix is used a benchmark to set the price of swaps and interest rate derivatives.

Bloomberg reports that the fine follows a ruling by US District Judge Jesse Furman in Manhattan that a group of investors led by an Alaska pension fund had raised "plausible allegations that a conspiracy among the defendants existed" and allowed the suit to go forward.

The pension funds and municipalities claim that from 2009 onwards the banks electronic chatrooms to fix the IDSAfix, typically submitting the same prices when it came time to fix the price.

Other bank defendants have yet to settle. HSBC, Morgan Stanley, BNP Paribas, Goldman Sachs, Nomura, UBS, Wells Fargo, and ICAP are still involved in the case, according to Bloomberg.

(Reuters reporting by Jonathan Stempel in New York; Editing by David Gregorio)