The FBI’s probe is said to focus on US citizens Ashish and Amol Gupta, the nephews of Atul and Ajay Gupta.
The Financial Times reports that US investigators are looking into individuals, bank accounts and companies in America for ties to alleged graft involving the Guptas.
In a separate and unrelated development, Britain’s banking regulator, the Financial Conduct Authority (FCA), announced it was in contact with two UK banks, HSBC and Standard Chartered over possible links with the controversial Gupta family.
“The FCA is already in contact with both banks named and will consider carefully further responses received,” the regulator said.
The British parliament is expected to discuss the issue on Thursday.
The Gupta empire which spans media, mining and consulting have been linked to a numerous leaked emails alleging graft in its dealings with South Africa’s state-owned companies.
There has been no comment from Gupta spokesman, Gary Naidoo. The Guptas deny any wrongdoing and they have not been convicted of any crime.
But Zweli Mkhize, one of several potential candidates to replace Zuma as head of the African National Congress in December said Washington and London were within their rights.
“If there is any information suggesting corruption or irregularities, it needs to be investigated across the borders. It should not be restricted to South Africa,” he told reporters.