In connection with the investigation, the bank has agreed to deposit a bail bond of 50 million euros (40 million pounds), it said in a statement on Friday, confirming a report in Le Monde newspaper.

The investigation follows the theft of personal details of HSBC private banking clients in Switzerland that were passed on to Belgian and French authorities in 2010. HSBC Private Bank was charged with tax fraud and money laundering in Belgium on Monday.

"We confirm that HSBC Private Bank (Suisse) SA has been placed under formal investigation by French magistrates who are examining whether the bank acted appropriately between 2006-07 in relation to certain clients of the bank who had French tax reporting requirements, as well as in relation to the way the bank offered its services in the country," HSBC Private Bank said in an emailed statement.

"We will continue to cooperate with the French authorities to the fullest extent possible," it added.

Countries around the world are trying to crack down on undeclared funds held in offshore havens, after the global financial crisis strained government budgets and made the need to maximise tax receipts more pressing.

France and Switzerland agreed in June to cooperate more closely on French efforts to crack down on citizens with hidden Swiss bank accounts to root out tax dodgers.

(Reporting by Chine Labbe and Dominique Vidalon; Editing by Natalie Huet)