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.
More top news
Plumbers and heating engineers should be trained to help people living in homes that are too cold, according to new health guidelines.
Rain for the northwest, dry and cold elsewhere
Rejecting a showdown with Ed Miliband, David Cameron's terms sent to broadcasters reveal his deep dissatisfaction with the debate proposals.