A US appeals court has revived private antitrust litigation accusing major banks of conspiring to manipulate the Libor benchmark interest rate, in a big setback for their defense against investors' claims of market-rigging.

The 2nd US Circuit Court of Appeals in Manhattan reversed a lower court judge's dismissal of investors' antitrust claims against 16 banks, including Deutsche Bank AG, UBS AG , Bank of America Corp and JPMorgan Chase & Co because she found no showing of anticompetitive harm.

"Appellants sustained their burden of showing injury by alleging that they paid artificially fixed higher prices," Circuit Judge Dennis Jacobs wrote for a three-judge appeals court panel.

Libor, or the London Interbank Offered Rate, underpins hundreds of trillions of dollars of transactions and is used to set rates on credit cards, student loans and mortgages. It is calculated based on submissions by banks that sit on panels.

But investors including the University of California and cities such as Baltimore, Houston and Philadelphia accused big banks of suppressing Libor during the financial crisis to boost earnings or make their finances appear healthier.

The decision could help investors in several lawsuits in Manhattan seeking to hold banks liable for billions of dollars in damages for alleged price-fixing in U.S. Treasuries, commodities, currencies, derivatives and other rates.

One such lawsuit, concerning credit default swaps, led to a $1.86 billion settlement last September with a dozen banks.

"It strengthens the hand of investors in other price-fixing cases based on benchmarks that were reached in collaborative, or outright collusive, arrangements," said Lawrence White, a professor at New York University's Stern School of Business.

Robert Wise, a lawyer at Davis Polk & Wardwell who argued the appeal on the banks' behalf, declined to comment.

"It's a long-awaited vindication of fundamental antitrust principles," said Michael Hausfeld, a lawyer for some plaintiffs in the Libor and other antitrust cases. "It establishes a roadmap for similar allegations in other cases involving benchmark rate-fixing by financial institutions."

LOOKING UNDER THE HOOD

Monday's decision overturned a March 2013 dismissal by US District Judge Naomi Reice Buchwald in Manhattan of antitrust claims that could justify triple damages.

Though she allowed lesser claims to proceed, Jacobs said the allegations suggested that the banks had crossed a line, turning their cooperative rate-setting process into collusion.

"The Sherman Act safeguards consumers from marketplace abuses," and Buchwald's dismissal of claims based on that antitrust law was "unsound," Jacobs wrote.

Monday's decision did not address the case's merits.

"It means the court is entitled to look under the hood," said Herbert Hovenkamp, an antitrust law professor at the University of Iowa. "The district judge got it wrong by adopting a categorical rule that because the banks were cooperating in setting Libor they could not be violating antitrust rules."

Michael Carrier, a Rutgers University law professor, said: "This decision is a reminder that price-fixing is taken very seriously, and is the most serious antitrust offense there is."

But Keith Hylton, a Boston University law professor, said the decision does not signal victory for investors in similar cases. "The likelihood of the plaintiffs actually having suffered harm is quite speculative in some of these," he said.

Some other banks that were sued are Barclays Plc, Citigroup Inc, Credit Suisse Group AG, HSBC Holdings Plc, Royal Bank of Canada, Rabobank BA , Royal Bank of Scotland Group Plc and Societe Generale.

The private litigation is separate from Libor rigging probes that have resulted in roughly $9 billion of sanctions worldwide, including $2.5 billion against Deutsche Bank in April 2015.

Several bank affiliates have pleaded guilty to criminal charges, and more than 20 people have been criminally charged.

Carrier, Hovenkamp and White endorsed a brief urging a reversal of Buchwald's ruling. Hylton endorsed a brief supporting the defendants. - Reuters