Swiss banking giant UBS could pay a fine of more than US$1 billion (A$ 950 million) to settle claims it manipulated the key Libor benchmark interest rate, reports said overnight.The Financial Times said UBS also won partial immunity from regulatory action by volunteering information in the developing global market scandal. Three men have been arrested this week over the issue, one a former UBS employee.The report comes less than six months after revelations that Barclays would pay a US$450 million (A$427 million) fine for rigging Libor. And it comes just two days after authorities said HSBC would pay US$1.92 billion (A$1.83 billion) over accusations it co-operated with money launderers in Mexico and terrorist financiers in the Middle East.Libor, the London InterBank Offered Rate, is the benchmark rate for banks borrowing from each other and underpins trillions of dollars of borrowings.