Swiss regulators said they are investigating several Swiss financial institutions for possible manipulation of foreign-exchange markets, an expansion of the latest probe into potential rigging of widely used market benchmarks.

Finma, which is Switzerland's main markets regulator, said it was working closely with authorities in other countries, "as multiple banks around the world are potentially implicated." The Swiss investigation comes after the UK's Financial Conduct Authority said in June that it was "aware of allegations" of efforts to rig currencies rates and was gathering information about potential manipulation of benchmark foreign-exchange rates.