"The (European) Commission has concerns that the three banks may have taken part in a collusive scheme which aimed at distorting the normal course of pricing components for euro interest rate derivatives," the EU competition authority said.
The three banks could face penalties of up to 10 percent of their global turnover if found guilty of breaching EU antitrust rules.
In December a record 1.7-billion-euro ($2.3 billion) fine was levied on six banks including Deutsche Bank, Royal Bank of Scotland and Citigroup for similar offences. The lenders settled their charges and received a 10-percent cut in their fines.
The Commission did not provide details about broker ICAP which is under investigation for suspected rigging of the yen Libor financial benchmark.
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