A U.S. appeals court on Friday upheld a 2013 ruling that UBS AG was not liable to shareholders for saying it was able to control risk even as a rogue trader caused $2.3 billion in losses.

Plaintiffs led by two pension funds in Elmsford, New York, claimed that before former UBS trader Kweku Adoboli's trades were revealed on Sept. 15, 2011, UBS officials had misled investors by frequently touting the Swiss bank's internal controls and "disciplined" risk culture.

Their case was first thrown out by U.S. District Judge Katherine Forrest in Manhattan in December 2013.

The pension funds appealed, but the 2nd U.S. Circuit Court of Appeals in New York said they failed to show that UBS intended to mislead them about its risk management, or that any shortcomings were severe enough to support a fraud claim.

"Plaintiffs have offered no plausible explanation as to why defendants would turn a blind eye to the possibility that unauthorized trading was exposing UBS to billions of losses," the court said in an unsigned order.

The losses stemmed from revelations about unauthorized and fictitious trades made by Adoboli who was convicted in November 2012 of fraud. Adoboli, a British trader born in Ghana, admitted at trial to making his trades to hide his risk exposures, but said he was trying to make money for the bank.

UBS highlighted the claim as outstanding in its fourth-quarter report, but did not disclose what if anything it had provisioned in case of any settlement.