A year-long review has found that 133 traders at 20 banks in Singapore tried to rig benchmark interest rates including one that affects the cost of home loans.

The Monetary Authority of Singapore also found that there were flaws in the banks' governance and surveillance systems involved in their benchmark submissions.

These benchmark rates included the Singapore Interbank Offered Rates (SIBOR) and Swap Offered Rates (SOR).

MAS announced on Friday that it will now require 19 of these banks to set aside deposits ranging from $100 million to $1.2 billion for a year at zero interest, depending on the severity of the deficiencies in their rate setting systems or the number of attempts made by their traders to rig the rates.

They have to deposit the funds with MAS within a month.

This means that the banks will lose out on whatever interest they may have earned from lending out that money.

UBS, ING and Royal Bank of Scotland have been asked to make the highest deposits of between $1 billion and $1.2 billion.

Bank of America, BNP Paribas and OCBC have been asked to set aside $700 million to $800 million each.

Seven other banks including DBS, Standard Chartered and UOB have to set aside $400 million to $600 million.

Another six including Citibank will set aside $100 million to $300 million.

Commerzbank is the only one that has not been asked to deposit any funds with the MAS.