US prosecutors are stepping up their criminal investigation into HSBC concerning its sale of offshore tax services, the New York Times reported, citing unnamed sources and court documents.

The report comes a few days after it was reported that the US Department of Justice was carrying out a criminal probe of the bank to catch alleged tax evaders, looking at account holders in locations including Singapore and India.

In the NYT news report, it said that at least two US clients of HSBC are aiding federal prosecutors by turning over account details, names of bankers and internal memorandums and other confidential documents regarding HSBC’s offshore private bank.

HSBC, which is listed in London, was not reachable for comment at the time WealthBriefing went to press. In the past, the bank has declined to comment on the issue.

The scrutiny of HSBC highlights how the US assault on suspected tax cheats has taken on a broader reach since the high-profile tussle between the US authorities and Swiss banking giant UBS last year. A number of governments, notably those of the US, Germany, France and the UK, have mounted aggressive campaigns to halt leakage of revenues to offshore financial centres, even resorting in some cases to paying for private client information stolen by ex-bank employees.

A source was quoted by the NYT as saying that HSBC, however, has not received a target letter from prosecutors indicating that a grand jury has been convened to investigate it. That would be the first step toward an indictment.

One of the people briefed on the investigation said the Justice Department “is looking for UBS-style numbers and UBS-style fact patterns, to see if there’s a UBS-style situation of a bank actively marketing” tax evasion services in the US, the report said.

Special agents from the Internal Revenue Service have paid surprise visits in recent weeks to at least two US clients of HSBC, the report said.

The pressure on such offshore accounts has already caused a number of banks to change their strategy. UBS, along with fellow Swiss banks Wegelin and Julius Baer, no longer provides offshore banking services to US clients. Meanwhile, in June, it was reported that Vontobel, another Swiss bank, had set up a unit to deal with US citizens who have declared Swiss accounts.