UBS said that United States and Japanese regulators were investigating whether the Swiss bank had tried to manipulate a benchmark used to set interest rates around the world.
The bank, based in Zurich, said in a statement on Tuesday that it had been subpoenaed by the Securities and Exchange Commission, the Commodity Futures Trading Commission and the Justice Department in connection with an investigation into whether the bank had tried improperly to influence the London Interbank Offered Rate, or Libor.
UBS said that the Financial Supervisory Agency in Japan was pursuing a similar line of inquiry and had ordered the bank to provide information.
Libor is a measure of how much banks charge each other for loans, and is a hugely important barometer of market interest rates and the health of the financial system.
Fluctuations in Libor affect the payments made by millions of homeowners and other borrowers.
A UBS spokesman said the bank had nothing to add beyond a one-paragraph disclosure in the annual report.
?UBS is conducting an internal review and is cooperating with the investigations,? the bank said. The British Bankers? Association, which sets Libor rates, said that it observed ?rigorous standards? and that its calculations were ?fully transparent.? The news of the probe was buried in UBS?s annual report, on Tuesday, the same day that Deutsche Bank issued its yearly report to shareholders.