LONDON - UBS suspended foreign-exchange traders in the United States, Singapore and Switzerland as its investigation into the alleged rigging of currency markets widened, according to a person with knowledge of the matter.

They include Mr Onur Sert, an emerging-markets spot trader based in New York, and at least three more worldwide, said the person, who asked not to be identified because of the probe.

Mr Sert and Mr Dominik von Arx, a spokesman for UBS in London, both declined to comment on the suspensions.

Switzerland's largest bank opened a review of its currency operations last year after Bloomberg News reported in June that traders in the industry had colluded to rig the WM/Reuters rates, a benchmark used by investors and companies around the world.

Sert, 30, previously worked for Standard Chartered.

UBS suspended Mr Niall O'Riordan, its co-chief dealer, last year after regulators announced they were probing the US$5.3 trillion-a-day market.

The Zurich-based firm has also banned employees from taking part in instant-message groups involving other banks.

Authorities in three continents are investigating whether traders at some of the world's largest banks sought to manipulate the WM/Reuters rates in their favor by pushing through trades before and during the 60-second windows when the benchmarks are set.

At least two dozen traders have been fired, suspended or put on leave by banks including Citigroup, Royal Bank of Scotland Group Plc and Barclays.

No firms or traders have been accused of wrongdoing by government authorities.