The European Commission said it is "determined to fight and sanction" rate-rigging cartels formed by some banks.
Vice president of competition policy Joaquin Almunia said:
Today's decision sends a clear message that the Commission is determined to fight and sanction these cartels in the financial sector.
Healthy competition and transparency are crucial for financial markets to work properly, at the service of the real economy rather than the interests of a few.
The sanctions - the first from the European Commission on rate manipulation - are the highest yet for European anti-trust enforcement.