Swiss banking giant UBS AG said Wednesday it has admitted to fraud and agreed to pay $1.5 billion to U.S., British and Swiss authorities in an investigation into the rigging of global benchmark interest rates.

The settlement caps a tough year for Switzerland's biggest bank, which is one of several leading banks that has been under investigation over allegations of manipulating the benchmark LIBOR interest rate, short for London interbank offered rate. It is used to set the interest rates on trillions of dollars in contracts around the world, including mortgages and credit cards.

The rate is a self-policing system and relies on information that global banks submit to a British banking authority. American and British regulators have already fined Britain's Barclays $453 million for submitting false information between 2005 and 2009 to keep the interest rate low.

UBS said some of its employees tried to rig the LIBOR rate in several currencies, but that its Japan unit, where much of the manipulation took place, entered a plea to one count of wire fraud in a the proposed agreement with the U.S. Justice Department.

The statement from the UBS board of directors said some of its personnel had "engaged in efforts to manipulate submissions for certain benchmark rates to benefit trading positions."

Staff 'colluded with employees at other banks'

The bank also said that some of its employees had "colluded with employees at other banks and cash brokers to influence certain benchmark rates to benefit their trading positions" or had given "inappropriate directions to UBS submitters that were in part motivated by a desire to avoid unfair and negative market and media perceptions during the financial crisis."

Sergio Ermotti, who was appointed CEO of UBS AG in November 2012 in the wake of a major trading scandal, said in the statement that the misconduct does not reflect the bank's values or standards.

"We deeply regret this inappropriate and unethical behaviour. No amount of profit is more important than the reputation of the firm, and we are committed to doing business with integrity," he said.

With more than 2.2 trillion Swiss francs ($2.4 trillion) in invested assets, Zurich-based UBS is one of the world's largest managers of private wealth assets. At last count, the bank had 63,745 employees in 57 countries and said it aims for a headcount of 54,000 in 2015.

Along with Credit Suisse, the second-largest Swiss bank, UBS is on the list of the 29 "global systemically important banks" that the Basel, Switzerland-based Bank for International Settlements, the central bank for central banks, considers too big to fail.

In 2008, UBS was forced to seek a bailout from the Swiss government when it was hard hit by the financial crisis and its fixed-income unit had more than $50 billion in losses. U.S. authorities fined UBS $780 million in 2009 for helping U.S. citizens avoid paying taxes. The U.S. government has since been pushing Switzerland to loosen its rules on banking secrecy and has been trying to shed its image as a tax haven, signing deals with the United States, Germany and Britain to provide greater assistance to foreign tax authorities seeking information on their citizens' accounts.

In April, Ermotti called Switzerland's tax disputes with the United States and some European nations "an economic war" putting thousands of jobs at risk.

In September 2011 the bank announced more than $2 billion in losses and blamed a 32-year-old rogue trader, Kweku Adoboli, at its London office for Britain's biggest-ever fraud at a bank.

Britain's financial regulator fined UBS, saying its internal controls were inadequate to prevent Adoboli, a relatively inexperienced trader, from making vast and risky bets. Adoboli has been sentenced to seven years in prison.