The spokesman for UBS-Europe confirmed the information reported by a German business magazine, which also reported that the homes of some 2,000 customers of the bank were also being searched.
The probe, launched Tuesday, was being led by investigators from the northwestern city of Bochum into the bank, formerly known as UBS-Luxembourg and which is headquartered in Frankfurt.
A spokesman for prosecutors cited by the magazine said "in-depth investigations are under way concerning a number of suspects throughout German territory."
Prosecutors suspect the holders of the accounts did not declare investment income not listed on tax declarations.
The probe was launched by German authorities based on information on some 2,000 bank clients purchased from an informant. UBS officials at the group's headquarters in Zurich declined to comment on Wednesday.
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