NEW YORK/LONDON (Reuters) - UBS AG has suspended four more of its traders in the wake of a global investigation into collusion and manipulation by big dealers in the foreign exchange market, Bloomberg News reported on Wednesday. According to the report, Onur Sert, an emerging markets trader in New York, was among the four the investment bank suspended. The report did not name the other three people, but said they were located in Singapore and Switzerland. A spokesman for UBS in London declined to comment. Authorities in the United States, UK, Switzerland, Germany and Singapore are looking into allegations of collusion and manipulation of the $5.3 trillion a day global forex market. Britain's market regulator began looking into such allegations at least as far back as early 2013 and formally announced it was investigating in October, the same month the U.S. Justice Department opened its own probe. Sources familiar with the matter told Reuters last month that UBS had approached U.S. authorities in September with information relating to their probe into alleged rigging of currency markets in the hope of gaining antitrust immunity if charged with wrongdoing. Since the probes began, more than 20 traders at some of the world's biggest banks have so far been placed on leave, suspended or fired. Regulators in the UK have said the forex investigation could be bigger than the Libor rate-rigging scandal, which has triggered criminal prosecutions as well as $6 billion in fines and settlements. (Reporting by Emily Flitter; Additional reporting by Jamie McGeever in London, editing by G Crosse)