WASHINGTON (Reuters) - Some 14,700 rich Americans worried about a US government crackdown on offshore tax cheats came forward to participate in a tax amnesty programme, the top US tax official said yesterday.

Participation in the Internal Revenue Service's amnesty programme was "unprecedented" and the final number was nearly double the agency's estimate in October, US Internal Revenue Service Commissioner Douglas Shulman told reporters in a telephone briefing.

The IRS amnesty programme, which ended in October, offered reduced penalties for wealthy Americans who voluntarily disclosed previously undeclared foreign bank accounts and assets. "We were flooded with people coming in the final days of the programme," Shulman said.

While agency officials were still analysing the amount of offshore assets and bank accounts disclosed, Shulman said "we are talking about billions of dollars coming into the US Treasury" from the amnesty programme.

Of the 14,700 newly disclosed accounts, Shulman said many involved bank accounts in Switzerland and Europe, but assets were also hidden in more than 70 countries.

"The whole game around bank secrecy, around offshore (tax) evasion is changing" because of pressure from the US Justice Department and from international capital markets, he said.

At the centre of the US efforts to combat tax evasion abroad is a case against Swiss banking giant UBS AG, which led the bank to agree to reveal the names of 4,450 client accounts. Shulman also said the outpouring of hidden offshore accounts does not affect in any way the obligation of UBS to turn over those American account-holder names.

Although the amnesty program has ended, Shulman encouraged Americans with hidden offshore assets to continue to come forward and talk with the IRS about them. "It will be much worse for them if we find them first," he said.