After four months of inquiries Geneva authorities closed their investigation last month after HSBC agreed to pay the fine.

Leaked files this year sparked allegations HSBC's private bank may have let clients conceal millions of dollars of assets and put Europe's largest lender in the spotlight of regulators including Geneva's public prosecutor.

Swiss newspaper SonntagsZeitung reported on Sunday that Tunisia, which is trying to recover funds linked to ousted autocratic leader Zine el-Abidine Ben Ali, had made an objection on June 16 to the settlement.

Yves Klein, a Geneva lawyer representing Tunisia, confirmed on Monday the submission to the Geneva Criminal Court of Appeal.

"The purpose of the appeal lodged by the Republic of Tunisia is just to protect its rights in the eventuality that they might be affected by the decision of termination of the criminal proceedings," he said in an emailed response to a query.

"The appeal procedure will allow to clarify the situation from a legal point of view."

A spokesman for HSBC declined comment.

When the settlement was announced, Olivier Jornot, Geneva's attorney general, told reporters the case had exposed the weakness of Swiss law in fighting the flow of criminal funds.

"It's easy to ask public prosecutors afterwards to carry out titanic investigations. But on the other hand when we have a law that practically doesn't punish intermediaries accepting money of dubious origin, there is a problem," he had said.

The bank said at the time that no criminal charges would be filed and that neither the bank nor its employees were suspected of any current criminal offences.

HSBC's Swiss arm is still facing investigations by U.S., French and Belgian authorities.

HSBC has apologised to customers and investors over the previous failings of its Swiss business and has said the operation has since been overhauled.

(Reporting by Michael Shields; Editing by Mark Potter)