The gold and silver fixes, along with other commodity benchmarks, have come under increasing scrutiny by regulators in Europe and the United States since a London Interbank Offered Rate (Libor) manipulation case in 2012.

The century-old gold fix is a standard price for the metal that banks set twice a day over the phone.

"We have a preliminary investigation into the manipulation of gold and precious metal price fixing," the spokesman said. He declined to say which banks were involved.

The spokesman said this preliminary investigation began in 2014, without elaborating.

It is unclear whether it started in March last year, when WEKO opened an investigation into possible collusion in the foreign exchange market by several banks.

This investigation is still ongoing, the spokesman said.

The Wall Street Journal reported the U.S. Department of Justice and the Commodity Futures Trading Commission are investigating at least 10 major banks, including Credit Suisse and UBS, for possible rigging of precious metals markets.

ICE Benchmark Administration will run an electronic gold price benchmark from March 20 to replace the London gold fix.

Manipulation in the precious metals market emerged as part of a probe into manipulation in the foreign exchange market, which in November resulted in regulators fining six major banks, including Zurich-based UBS, a total of $4.3 billion.

FINMA, Switzerland's financial watchdog, said in November it had found a "clear attempt" to manipulate precious metals price benchmarks during a cross-market investigation into trading at UBS.

A spokeswoman for UBS declined to comment on WEKO's preliminary investigation.