NEW YORK -- European regulators have fined eight major financial firms $2.3 billion for rigging key interest rates, the latest major penalty in a continuing worldwide fixing probe.

Two major American banks, JPMorgan Chase and Citigroup, were among the institutions hit with penalties, which the European Commission announced Wednesday in Belgium.

"What is shocking about the `rate-rigging~ scandals is not only the manipulation of benchmarks, which is being tackled by financial regulators worldwide, but also the collusion between banks who are supposed to be competing with each other," Joaquin Almunia, the commission's vice president in charge of competition policy, said in a statement.

Central to the case are key interest rates that help form the foundation of the global financial system. The London Inter-Bank Offered Rate, known as Libor, determines how much banks pay to lend to each other. Trillions of dollars in financial products are pegged to these rates.

The fines, totaling 1.7 billion euros, were also levied against Deutsche Bank, Societe Generale, Royal Bank of Scotland, and RP Martin. Barclays and UBS avoided fines in exchange for their cooperation.

Citigroup, which also aided the commission's investigation, avoided additional fines of 55 million euros on top of the 70 million euros it will pay.

JPMorgan faces a fine of about 80 million euros. In a statement, the bank said the case involved the conduct of two former traders during a one-month period in early 2007.

"The settlement makes no finding that JPMorgan Chase management had any knowledge or involvement in the conduct at issue, or that the traders' actions had any impact on the firm's Libor submissions or the published Libor rates," the bank said.

Deutsche Bank is on the hook for a much larger chunk of the total fine: 725 million euros.

Jürgen Fitschen and Anshu Jain, co-chief executives of Deutsche Bank, said traders' past conduct amounted to a "gross violation of Deutsche Bank's values and beliefs."

"We are attaching the highest institutional importance to ensuring that this type of misconduct does not happen again," they said in a statement.

EU regulators said Wednesday they would continue investigating the conduct of traders at Credit Agricole, HSBC and JPMorgan.

JPMorgan said it has cooperated fully and does not believe that it engaged in wrongdoing involving the Euro Inter-Bank Offered Rate, or Euribor, benchmark interest rate.