Mitsubishi UFJ Financial Group said it has fired an employee who allegedly stole as much as ¥2 billion ($13 million) from the safe deposit boxes of approximately 60 clients.

The theft took place at two branches in Tokyo over 4½ years before it was discovered on Oct. 31, MUFG’s main banking arm said in a statement on Friday. Japan’s biggest bank is investigating the incident and consulting with the police, it said.

The front-line employee was responsible for managing the safe deposit boxes and "took advantage of this position” to open them without permission, the bank said. The market value of the damages was ¥1 billion to ¥2 billion. The person has admitted to the wrongdoing and has been dismissed.

"This act not only undermines the trust and confidence that customers have placed in us but also shakes the very foundation of our business,” MUFG said, adding that there were no similar incidents in other branches.

The bank is "considering and will swiftly implement appropriate compensation” for damages incurred by clients as well as measures to prevent a recurrence, it added.

MUFG is the latest major Japanese financial firm to reveal alleged crimes committed by rank-and-file staff. Nomura Holdings said this week that a former employee has been charged on suspicion of robbery, attempted murder and arson after he allegedly drugged and stole cash from an elderly client at their home in Hiroshima.