Deutsche Bank
Deutsche Bank is one of the many banks under investigation for potential Libor and Euribor fixing Reuters

The UK's Serious Fraud Office have called in former traders at Barclays Deutsche Bank for questioning over concerns that a key borrowing benchmark was manipulated.

The SFO is investigating whether Euribor, the Euro interbank lending rate, was rigged to benefit individual traders or institutions' positions, the FT reported.

The agency has already charged 13 people with manipulation in its investigations into whether Libor, the London interbank offered rate, was manipulated. Its investigation into Euribor, the Brussels equivalent of Libor, began in 2012 and has yielded few tangible results.

Both banks are facing class-action lawsuits in the United States over allegations they manipulated Euribor. The cases are due to be heard in May 2015.

Barclays has set aside £750m for fines arising from allegations over rigging foreign exchange markets and said last week that it hopes that investigations are settled as soon as possible.

Deutsche Bank is ready to pay around €1bn for fines related to Libor rigging allegations.