The U.S. Justice Department has opened about 100 criminal investigations into wealthy American clients of the Swiss bank UBS AG , the New York Times said, citing a person briefed on the matter.

Several accounts under scrutiny have more than $100 million in assets, with the single largest holding more than $150 million, the paper said.

A UBS spokesman in Hong Kong told Reuters that the bank does not comment on market speculation or rumor.

The U.S. Justice Department could not be immediately reached for comment.

UBS, in February, acknowledged responsibility for helping U.S. clients conceal assets from the U.S. government. The Swiss bank also agreed to pay a $780 million fine, and to identify some U.S. clients.

U.S. authorities, fearing that the agreement might yield very few names, then filed the civil lawsuit against UBS.

UBS has argued that the information sought by the United States is protected by Swiss financial privacy laws and has refused to disclose the names of tens of thousands of its U.S. clients.

(Reporting by Ajay Kamalakaran in Bangalore; Editing by Lincoln Feast)