US regulators probe BofA, Citi and Barclays over improper borrowing rates

US regulators serviced Bank of America, Citigroup and Barclays with subpoenas over the investigation into the setting of the London interbank offered rate, or Libor, for U.S. dollars between 2006 and 2008, the Financial Times said.

UBS was among other banks who received subpoenas from US and Japanese regulators over whether it made "improper attempts" to manipulate LIBOR rates, the benchmark price for interbank borrowing costs.

The Financial Times said the regulators are narrowing the probe to a handful of banks among the 16 that help the British Bankers' Association (BBA) set LIBOR rates.