The bank, which is heavily implicated in a scandal surrounding former budget minister Jérôme Cahuzac, stressed that it "has no French resident holding or having held political duties in France among its clients."

Cahuzac resigned in disgrace in March over an undeclared foreign bank account said to contain around €600,000 ($770,000).

He is facing charges of tax fraud, while his wife Patricia Cahuzac was also taken into custody this week and questioned by anti-fraud police before being freed Thursday, a source close to the investigation said.

Cahuzac's account is believed to have resided for a time with Reyl before the bank in 2009 helped Cahuzac transfer the funds to Singapore to avoid detection by French tax authorities.

A former official with the bank, Pierre Condamin-Gerbier, who has claimed to know of 15 French politicians and "big names" with undeclared bank accounts in Switzerland, said Wednesday he had handed the information over to French investigators.

Condamin-Gerbier has worked for several other Swiss financial institutions and he did not specifically link the politicians with the Reyl bank.

However, according to news reports, he also provided detailed accounts of how the bank helped rich French entrepreneur Alexandre Allard, who had been living abroad, to minimize his fortune of several hundreds of millions of dollars when he brought it back to France in a bid to dodge taxes.

"The Reyl Group would like to formally deny all of the allegations against it of an accusatory nature published by French and Swiss media over the past 48 hours," the bank said in a statement, without providing further details.