(Bloomberg News) Wegelin & Co., the 270-year-old private bank, became the first Swiss lender to face criminal charges in a broadening U.S. crackdown on offshore firms suspected of helping Americans evade taxes.

Wegelin helped Americans hide more than $1.2 billion in assets and evade U.S. taxes, according to an indictment filed yesterday in federal court in New York. The new charges expand on earlier ones filed Jan. 3 against three bankers at Wegelin's Zurich branch accused of conspiring to help U.S. clients cheat on their taxes.

Prosecutors said that from 2002 to 2011, more than 100 U.S. taxpayers conspired with Wegelin, the three Zurich bankers -- Michael Berlinka, Urs Frei and Roger Keller -- and others. The bank held more than $1.2 billion in assets not declared to the Internal Revenue Service, according to the indictment.

"Wegelin Bank aided and abetted U.S. taxpayers who were in flagrant violation of the tax code," Manhattan U.S. Attorney Preet Bharara said in a statement.

The U.S. and Switzerland are in talks to resolve a U.S. probe of offshore tax evasion. Wegelin was one of at least 11 banks under criminal investigation by the Justice Department's tax division.

Wegelin announced on Jan. 27 that it agreed to a sale to Switzerland's Raiffeisen Group.

Bryan Skarlatos, a tax attorney in New York, said the indictment is an important step because it demonstrates the government's willingness to indict a foreign bank.

"The indictment shows that the U.S. government will indict a Swiss bank if they don't get cooperation," said Skarlatos of Kostelanetz & Fink LLP. "It's symbolic in that the United States is saying that if a Swiss bank doesn't cooperate, it will be indicted. It puts pressure on other Swiss banks to cooperate."

Federal authorities yesterday also seized $16 million in Wegelin's correspondent bank account in the U.S. at UBS AG.

Richard Strassberg, a lawyer who represents the bank in the U.S., declined to comment.