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.