HSBC's Indian banking unit is at the heart of fresh revelations around tax evasion, days after a global expose showed tax dodging through accounts in the British major's Swiss banking unit, a media report said on Sunday. It is alleged that representatives of HSBC India, which has employees based in America, assured customers that details of their accounts would not be reported to tax officials.

The latest revelations came even as the bank issued full- page advertisements in British newspapers as a public apology after reports that its Swiss banking arm had helped some wealthy clients avoid tax. According to court documents seen by The Sunday Times, employees in one case allegedly advised a New Jersey Indian- origin businessman to transfer funds in tranches of under 6,500 pounds to "stay below the radar".

Court documents reveal that HSBC India has been accused of helping American citizens of Indian-origin to avoid tax, the report said. The American justice department issued a summons against the bank in April, 2011 to reveal details of clients. It was claimed that the bank promoted its services on the basis of keeping information secret from the tax authorities.

"Prospective clients were told that, as a foreign bank, HSBC India would not disclose the accounts to the IRS (Inland Revenue Service)," the government said in court filings. "The IRS has learnt that thousands of United States taxpayers with accounts at HSBC India may have failed to disclose those accounts, and report income on them, as required by law," it said.

The bank was said to have had 9,000 American residents of Indian-origin but fewer than 1,400 had disclosed the existence of their accounts.

In another case, HSBC India representatives are alleged to have advised New Jersey businessman Vaibhav Dahake to transfer money in batches of 6,500 pounds to "stay below the radar". The bank officials are alleged to have "advised and assisted" in tax evasion.

Dahake admitted concealing undeclared bank accounts in 2011, but said bank representatives had solicited him to open accounts that paid high interest rates and would not be declared to tax officials.

HSBC has been at the centre of a major storm after files were exposed by Herve Falciani, who started working for the HSBC private bank in Geneva in 2006. The whistleblower has said the UK government should have known about the scandal in 2010. The UK's Treasury Committee will conduct an inquiry into the claims.

The British bank has taken out advertisements this weekend apologising for past compliance failures and assuring customers that the bank had "no appetite to do business with clients who are evading their taxes". The advert reproduces an open letter signed by chief executive Stuart Gulliver, which says recent coverage had been "a painful experience".

It reads: "The media focus has been on historical events that show the standards to which we operate today were not universally in place in our Swiss operations eight years ago. "We must show we understand that the societies we serve expect more from us. We therefore offer our sincerest apologies."

On Saturday, HSBC's former chief executive and chairman Stephen Green, who was at the centre of the SwissLeaks tax scandal, stepped down from his role at finance lobby group TheCityUK.