Singapore's central bank censured a record 20 banks after it found more than 100 traders in the city state tried to rig key borrowing and currency rates.
The probe by the Monetary Authority of Singapore (MAS) marks the latest development in a global crackdown on rate-rigging and adds more banks, including ING and Bank of America , to the list of lenders involved.
The watchdog said on Friday that 133 traders had tried to inappropriately influence the rates. It did not fine the banks, but ordered them to set aside additional reserves for a year.
The city state's banking and market associations also unveiled reforms of how banks will set the benchmarks, including basing some of them on actual trades rather than estimates submitted by banks. Europe and the United States are also pushing for benchmark rates to be based on actual trades.
Financial market reference rates are under intense scrutiny around the world following the discovery that some had been rigged, most notably the Libor - London Interbank Offered Rate - benchmark for interest rates.
Barclays was the first bank to be fined for Libor manipulation, and US and UK authorities have slapped fines of hundreds of millions of dollars on Royal Bank of Scotland and UBS and are investigating more banks.
The regulatory focus has now expanded to the foreign exchange market. Britain's financial watchdog is looking into a report that traders manipulated benchmark foreign exchange rates.
The Singapore watchdog ordered UBS, RBS and ING to set aside the most in additional reserves, with each having to post between S$1 billion ($800 million) and S$1.2 billion extra with the central bank.
The money will be returned if the banks take the required remedial action.