Seven former U.S. clients of UBS AG were charged with failing to pay taxes for assets held offshore in Swiss accounts, with one attempting to evade tax on $20 million, according to court documents on Thursday.

The cases are the latest in a slew the government has brought against former clients of the Swiss banking giant, after the bank last year admitted it actively helped Americans evade taxes overseas.

Four indictments, one criminal complaint and two other documents accuse a total of seven of tax evasion, according to documents filed in U.S. District Court for the Southern District of New York.

One client, New York lawyer Kenneth Heller, earned at least $7.1 million in unreported income from Swiss-based accounts in 2006, 2007 and 2008, such that he evaded about $2.3 million in taxes.

Heller was also accused of moving $20 million from UBS to another Swiss bank to avoid paying taxes.

UBS last year paid $780 million to settle a United States government lawsuit against it. As part of that deal, the bank handed over details on more than 250 accounts.

These cases are now being prosecuted by government lawyers.

Officials want to call attention to taxpayers' obligation to report assets held offshore ahead of Thursday's April 15 tax-filing deadline.

(Reporting by Grant McCool in New York and Kim Dixon in Washington; Editing by Maureen Bavdek)