Investigators from the US Internal Revenue Service (IRS) are looking into whether a Singapore asset management firm accepted transfers from undeclared Swiss accounts closed by American taxpayers, the Wall Street Journal (WSJ) said.
Lawyers who spoke to the paper on condition of anonymity said a handful of clients were being questioned about the asset manager. The report did not name the firm.
The Journal's online report on Sunday said the probe marks an expansion of the US crackdown on undeclared offshore accounts that began in Switzerland in 2009.
Since then, US officials have pursued banks and individual "enablers", such as lawyers or asset managers, that have helped American taxpayers hide money abroad in Switzerland, Liechtenstein, Israel, India and the Caribbean.
But until now, "there was little indication they had widened their probe to South-east Asia or Hong Kong", the Journal said.
The newspaper quoted Mr Bryan Skarlatos, a lawyer with Kostelanetz & Fink in New York, as saying that the IRS and US Justice Department "seem be turning their focus East, where there are many US taxpayers with accounts".
The law firm has represented nearly 2,000 American taxpayers with undeclared offshore accounts, the WSJ added.
Since the US crackdown on offshore account tax evasion began in 2009, more than 50,000 people have entered a special IRS limited amnesty programme for individuals with offshore accounts.
They have paid more than US$7 billion (S$9.6 billion) to the US authorities to resolve their cases, while banks in Switzerland and elsewhere have paid more than US$4 billion to resolve theirs, with more to come, the paper added.
The United States had, in 2011, started probing other banks and their involvement in offshore tax services after Swiss bank UBS admitted to helping Americans stash their assets overseas tax free.
The bank was fined US$780 million by the US in 2009.
Swiss banks reached an agreement to avoid prosecution if they reveal names of US citizens holding accounts with them, but they could still be fined up to half of the customer's asset value.