European Union antitrust regulators are examining whether banks manipulated the daily London interbank offered rate, according to two people familiar with the probe.

The European Commission sent banks requests for information last month on how rates are calculated, according to the people who declined to be identified because the discussions are private.

The EU probe into Libor adds to U.K. and U.S. financial regulators’ inquiries into the possible breach of rules governing the benchmark borrowing rate. Barclays Plc, the U.K.’s third-largest bank by assets, said last week that it was cooperating with U.S. and British regulators on their Libor investigations.

EU regulators last week opened an antitrust investigation into Goldman Sachs Group Inc., JPMorgan Chase & Co. and 14 other investment banks over agreements in the market for credit- default swaps that may harm competition.

Amelia Torres, a spokeswoman for the Brussels-based commission, declined to comment on the Libor probe.

UBS AG, Switzerland’s biggest bank, said in March it received demands for information from U.S. and Japanese authorities investigating possible attempts to manipulate the setting of Libor.

Libor Rates

Libor rates, a benchmark for more than $350 trillion of financial products worldwide, are set daily by the British Bankers’ Association based on data from banks reflecting how much it would cost them to borrow for various periods of time and in different currencies.

JPMorgan, Deutsche Bank AG, Royal Bank of Scotland Group Plc, Commerzbank AG, Lloyds Banking Group Plc, Credit Suisse Group AG, UBS, Credit Agricole SA and WestLB AG declined to comment.

Rabobank Groep spokesman Kees Nanninga said the Utrecht, Netherlands-based bank does “not comment on specific regulatory matters.”

Three calls and an e-mail to Barclays’ press office and two calls to HSBC Holdings Plc’s press office were unanswered on a U.K. holiday. The BBA in London didn’t respond to three calls seeking comment.

Societe Generale SA and BNP Paribas SA said they couldn’t immediately comment.

Lawrence Grayson, a spokesman for Charlotte, North Carolina-based Bank of America Corp., declined to comment.