As US lawmakers kept up their focus on the alleged wrongdoings involved in offshore bank accounts, New York Mayor Michael Bloomberg has said there is nothing wrong with his money managers investing money in such accounts, saying it enhances returns for his philanthropic organisation, reports said.

The billionaire media tycoon’s foundation has transferred some $400 million to offshore funds in widely known tax-sheltering countries like the Cayman Islands, Cyprus, Mauritius and Bermuda, according to the Bloomberg Family Foundation's tax forms.

Bloomberg's money is invested through a blind trust that prevents him from knowing his specific holdings, but he signs the tax returns that clearly list the overseas funds.

"I don't have any control over where my investments go," Bloomberg was quoted to have said.

"And incidentally, as far as I know, the investments that my money managers make are perfectly legal, they're fully disclosed and they're appropriate to maximize the assets which I'm giving away to charities," he told reporters.

Offshore banking has become a hot-button issue in US politics. The US administration last year reached a deal with the Swiss government, for example, under which UBS, the Swiss banking and wealth management group, transferred details on US client accounts to the US tax authority. Leigslators recently passed the HIRE Act, which contained provisions which impose further requirements on firms dealing with expat US citizens in order to catch potential tax evaders.

Defenders of international financial jurisdictions have argued that political pressure against so-called tax havensd is a form of protectionism and a way by which high-tax governments try to prevent healthy "tax competition". It has also been pointed out that on some definitions, the tiny US state of Delaware is a prime example of a tax haven.