The U.S. Internal Revenue Service (IRS) is preparing to pursue other foreign banks for allegedly facilitating tax evasion by wealthy Americans following its high-profile case against Switzerland's UBS AG , an IRS official said on Monday.

UBS, Switzerland's largest bank, in February acknowledged that it helped U.S. clients conceal assets from the U.S. government. It agreed to pay a $780 million fine and identify some of its American clients.

But U.S. authorities are still going after the Swiss bank, seeking to access the data of another 52,000 Americans they say are hiding about $14.8 billion in Swiss bank accounts.

We are developing John Doe summonses on other banks, Daniel Reeves, an agent with the IRS' Offshore Compliance division, told Reuters on the sidelines of a conference in Miami on offshore finance.

He was referring to the kind of subpoena filed by the IRS against UBS seeking to force the bank to turn over the names of clients suspected of evading U.S. taxes.

Reeves declined to say which, or how many, other banks could face cases filed by the IRS, but he confirmed the entities being investigated were foreign-based like UBS.

We have identified other offshore banks that are engaged in similar activities, he earlier told the conference.

On April 2, U.S. authorities arrested and charged an accountant in Florida in the first of what they said could be a series of tax evasion prosecutions of American clients of UBS.

Almost two weeks later, a wealthy Florida yacht broker pleaded guilty to using an account with UBS to hide more than $3 million in assets from the U.S. government.

$100 BILLION EACH YEAR

The IRS has pushed ahead with the prosecutions at a time when political leaders both in the United States and elsewhere are calling for a crackdown on tax havens and offshore centers where individuals and companies can hide away funds.

In the U.S., we're losing about $100 billion a year, because of tax evasion and other abusive practices, Robert Roach, counsel and chief investigator for the U.S. Senate Permanent Subcommittee on Investigations, said at the Miami conference.

This Senate subcommittee has been lobbying for more aggressive official action against tax havens and tax evasion, which Roach described as a rats' nest of problems.

Switzerland, which is seeking to defend its long-standing tradition of strict bank secrecy, asked the United States at the weekend to drop the case against UBS in return for a new tax accord the two countries are about to negotiate.

Swiss President Hans-Rudolf Merz said the request was made to U.S. Treasury Secretary Timothy Geithner on the sidelines of the International Monetary Fund's semi-annual meetings in Washington.

(Reporting by Tom Brown, Writing by Pascal Fletcher; Editing by Kenneth Barry)

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