Credit Suisse spokesman David Walker declined to say how many accounts it has handed over or to comment further.

"The U.S. tax matter and data handover is advancing faster than expected, which we believe is positive for Credit Suisse," Teresa Nielsen, a Zurich-based analyst at Vontobel Holding AG, wrote in a note to clients today.

Credit Suisse booked 295 million francs ($329 million) of litigation provisions for tax matters in the U.S. in the third quarter.

The government is dealing with an IRS request for administrative assistance relating to tax fraud, according to Mario Tuor, a spokesman for Switzerland's State Secretariat for International Financial Matters. He declined to comment on the number of fraud cases and when they occurred.

The Swiss Federal Tax Administration, which will collect the data from Credit Suisse, wasn't immediately available to comment.

Account holders who contest the handover of their data must notify the U.S. Justice Department they are appealing, according to the client letter.

Switzerland, the world's biggest center for offshore wealth, agreed in 2009 to meet international standards to avoid being blacklisted as a tax haven by the Organization for Economic Cooperation and Development. The London-based Tax Justice Network ranks Switzerland at the top of its 2011 financial secrecy index.

In February 2009, UBS AG, the biggest Swiss bank, avoided criminal prosecution by paying $780 million, admitting it fostered tax evasion and giving the IRS data on more than 250 accounts to avoid criminal prosecution. It later turned over data on another 4,450 accounts and in October 2010, the U.S. dropped its criminal case against UBS.

The Justice Department is pursuing new criminal cases against Swiss banks after American customers provided information on them through a U.S. voluntary-disclosure program.

The U.S. crackdown against offshore tax evasion has led to charges against UBS AG, at least 21 foreign bankers, advisers and attorneys and at least 36 U.S. taxpayers.