The investigation has been widened because Swiss bankers have advised clients to put assets into banks in other nations rather than report them to the US authorities, the newspaper said. The US Justice Department and Internal Revenue Service have received information about accounts at Bank Leumi in Israel and China Merchants Bank, it said, according to one of its sources. The US has not alleged either bank was engaged in wrongdoing. Bank Leumi said it was not aware of the investigation. A China Merchant Bank representative referred calls for information to its office in China.

Last week, four Credit Suisse bankers were indicted on charges of helping tax evaders. This bank has said it is not under investigation and is co-operating with the inquiry.

A number of banks, such as UBS, Wegelin and Julius Baer, have stopped providing offshore banking to US citizens, as authorities have mounted an increasingly determined effort to clamp down on alleged tax evasion. The most high profile case has concerned that of UBS, which in 2009 was embroiled in a civil and criminal case concerning tax evasion by former clients. In this bank’s case, it has handed over data on thousands of client accounts to the US.

Another lawyer said clients had voluntarily disclosed offshore accounts in New Zealand, Australia, India, the Bahamas, the Cayman Islands and the Channel Islands.