WASHINGTON - A group of Senate Democrats is urging the U.S. Department of Justice and federal banking and securities regulators to investigate allegations that domestic and foreign banks manipulated the London Interbank Offered Rate, or Libor, which is used as a benchmark in municipal bond-related swaps and other financial products.

"We urge you to direct your staff to thoroughly investigate the banks and the process involved in setting Libor for any wrongdoing," said the senators in identical letters sent Thursday to U.S. attorney general Eric Holder and members of the Financial Stability Oversight Council. "Banks and their employees found to have broken the law should face appropriate criminal prosecution and civil action."

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