NEW YORK (Reuters) – Seven former US clients of UBS AG were charged with filing false tax returns, collectively hiding more than $100 million held offshore in Swiss accounts.

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

Two of the seven pleaded guilty yesterday in Manhattan federal court.

"For the years 2003 to 2007, I filed a false income tax return knowing that it did not mention a UBS account I controlled or any income I earned in that account," one of the defendants, Jules Robbins, told US Magistrate Judge Ronald Ellis.

Robbins, a resident of New York who owned and operated companies that distributed watches, was believed to have had as much as $40 million in the account. Robbins agreed to pay a civil penalty of $20.8 million and faces a possible prison sentence of between six months and 12 months following his guilty plea.

Another of those charged, New York investment portfolio manager Federico Hernandez, pleaded guilty to similar charges before US District Judge Denny Chin. He faces a possible prison sentence of between 18 months and 24 months and a civil penalty of $4.4 million.

A US grand jury returned indictments against four other former bank clients, businessmen Ernest Vogliano, Shmuel Sternfeld, Richard Werdiger and a New York woman identified as Sybil Nancy Upham. US prosecutors also charged a disbarred lawyer, Kenneth Heller.

Their lawyers were not immediately known.

US prosecutors said in a statement that collectively, the seven hid more than $100 million from the Internal Revenue Service by using sham companies to conceal ownership of secret Swiss bank accounts at UBS.

Officials want to call attention to taxpayers' obligation to report offshore assets as the midnight April 15 deadline for filing tax returns looms.

Although keeping money offshore is not illegal, US taxpayers must report assets held there. For assets over $10,000 there is an additional reporting requirement with the US Treasury.

Several defendants used transfers of small bits of money to evade taxes, including a meeting where Vogliano asked his UBS financial advisor to prepare $100,000 in American Express Travelers checks in $500 denominations.

Heller took his money out of UBS after the United States started pursuing the bank in several states for mortgage-backed securities fraud, the court papers said. His UBS adviser, a friend of 20 years, helped him move the funds by avoiding reporting requirements.

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 US government lawyers.