Six financial institutions were fined €1.71 billion ($2.32 billion) by European Union regulators Wednesday for colluding in an attempt to manipulate key benchmark interest rates, the EU's largest-ever penalty in a cartel case.

The settlements involved penalties against some of the world's biggest banks, including Deutsche Bank, Societe Generale, Royal Bank of Scotland Group and JP Morgan Chase. The action brings to roughly €6 billion the total penalties levied by regulators against financial institutions in connection with probes into manipulation of the London interbank offered rate, or Libor, and other widely used financial benchmarks.