LONDON - A former Citigroup trader is among three people held in the first British arrests as part of global probes into tampering with the London interbank offered rate, according to two people familiar with the matter.

Thomas Hayes, a former trader at UBS AG and Citigroup, was arrested by the Serious Fraud Office and City of London Police on Tuesday, said the people, who asked not to be identified citing the continuing investigation. The other two men arrested worked at brokerage firm RP Martin Holdings, according to one of the people and a third person familiar with the investigation, who also requested anonymity.

The three men who were arrested, ranging in age from 33 to 47, are all British nationals living in Britain and were taken to a London police station for questioning, the SFO said in an e-mailed statement.

Global authorities are investigating claims that more than a dozen banks altered submissions used to set benchmarks such as Libor to profit from bets on interest-rate derivatives or make the lenders' finances appear healthier. Swiss lender UBS is expected to face a fine as early as this week that may surpass the record 290 million pounds ($466.6 million) paid in June by Barclays Plc, Britain's second-biggest bank, to settle claims it attempted to manipulate Libor.

The agency and police also searched three homes in Surrey and Essex, according to the SFO statement. Arrests in Britain are made early in investigations, allowing people, who may not be charged, to be questioned under caution.

Libor, a benchmark for more than $300 trillion of financial products worldwide, is derived from a survey of banks conducted each day on behalf of the British Bankers' Association in London. The rates help determine borrowing costs for everything from mortgages to student loans.

Hayes, a Tokyo-based trader for Citigroup, was previously dismissed for suspected involvement in the rate manipulation, a person familiar with the situation said earlier this year.

Jeff French, a spokesman for Citigroup in London, declined to comment or provide contact information for Hayes. A number for Hayes couldn't immediately be located.

Criminal probes by the SFO and U.S. Department of Justice are running in parallel with civil investigations being conducted by the Justice Department's fraud division, the U.S. Commodity Futures Trading Commission and the U.K. Financial Services Authority.