The Swiss Competition Commission COMCO said in a statement that it had received information regarding potential unlawful agreements among banks.

“Specifically, collusion between derivative traders might have influenced the LIBOR (London Interbank Offered Rate) and TIBOR (Tokyo Interbank Offered Rate) reference rates.

“Derivative traders working for a number of financial institutions might have manipulated these submissions by coordinating their behaviour, thereby influencing these reference rates in their favour,” the statement said.

The commission said derivative traders might have colluded to manipulate the difference between “the ask price and the bid price (spread) of derivatives based on these reference rates to the detriment of their clients.”

COMCO has begun to probe actions by Switzerland’s two biggest banks, UBS and Credit Suisse, as well as those of a dozen major foreign financial institutions and other companies.

A UBS spokeswoman contacted by AFP said the bank would “take very seriously” the investigation and will “cooperate fully” with authorities.

Foreign banks being investigated include the Bank of Tokyo-Mitsubishi, Citigroup, Deutsche Bank, HSBC, JP Morgan Chase, Mizuho Financial Group, Rabobank, Royal Bank of Scotland, Societe Generale and Sumitomo Mitsui Banking Corporation.

Tibor and Libor rates are based on central bank reference rates and determine the level of interest paid by participating financial institutions on interbank markets in London or Tokyo.

The rates are then used as benchmarks in many contracts and financial products such as home mortgages.

In December, Japan’s financial watchdog ordered a temporary suspension of trading activities at Japanese subsidiaries of the US bank Citigroup and UBS, accusing them of trying to manipulate interbank rates.

The Financial Times reported in March that US, Britain and Japanese officials had launched a probe that applied to all banks regarding the calculation of Libor for dollar interbank loans between 2006 and 2008.