Swiss regulators are investigating a number of financial firms over the potential manipulation of currency markets, where £3tn changes hands every day.
The regulator said that multiple banks around the world could be drawn into the investigation, which will raise fresh questions about the integrity of the markets.
The Swiss Financial Market Supervisory Authority said in a brief statement: "Finma is currently conducting investigations into several Swiss financial institutions in connection with possible manipulation of foreign exchange markets. Finma is co-ordinating closely with authorities in other countries as multiple banks around the world are potentially implicated."
The regulator said it would give no further details on the investigations or the banks potentially involved.
In June the UK's Financial Conduct Authority, the City regulator, also launched an investigation into potential rigging of currency markets, and the role of benchmarks, in some of the most liquid and actively traded markets in the world.
The role played by benchmarks in financial markets has been highlighted since the Libor-rigging scandal exposed traders at banks and financial firms around the world manipulating the key standards for interest rates. Barclays was the first major bank to be fined, paying £290m in June last year, but others have since followed including Royal Bank of Scotland, UBS and more recently the interdealer broker Icap.
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