Citigroup was forced to write off $50m after two traders accused of attempting to influence global lending rates left the bank, according to people familiar with a worldwide investigation that is gathering pace.

Nine separate enforcement agencies in the US, Europe and Japan have been probing whether big US and European banks manipulated the London Interbank Offered rate or Libor, the benchmark reference rate for $350tn worth of financial products, and other interbank lending rates.

So far, only Japan’s Financial Services Agency has formally sanctioned banks in connection with the probe. In December, regulators found that two former Citigroup employees in Tokyo attempted to pressure colleagues and employees at other banks involved in the rate-setting process for the Tokyo Interbank Offered Rate, or Tibor.