Switzerland's chief negotiator in the UBS AG tax case said that the Internal Revenue Service may request the names of American clients from other banks after the Swiss government agreed to hand over UBS account details.

"It is possible that the IRS will ask for more data on U.S. customers at other Swiss banks," Michael Ambuehl, who led discussions for the Swiss Foreign Ministry, said in written comments to Bloomberg News.

A disclosure similar in scope to the Aug. 19 agreement is "questionable" because UBS is the only Swiss bank to admit unlawful behavior in its efforts to win rich U.S. clients, Ambuehl said.

The IRS plans to target more banks, law firms and entities that help Americans hide assets, IRS Commissioner Douglas Shulman said when the settlement was announced. While Swiss banks manage about 27% of the world's offshore wealth, tax evasion through offshore accounts siphons $100 billion from tax revenue annually, according to U.S. officials.

UBS agreed to provide Swiss authorities with details of 4,450 accounts where "tax fraud or the like" is suspected. Though Switzerland has a year to decide which data to pass on to the IRS, legal appeals may delay the transfer beyond that period, according to Folco Galli, a spokesman for the Swiss Justice Ministry.

UBS admitted in February to participating "in a scheme to defraud the U.S." The Zurich banking company agreed to pay $780 million and disclose the names of more than 250 clients who allegedly hid assets from the IRS. A day later the IRS sued UBS for information on as many as 52,000 account holders, triggering negotiations that were settled last week.

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