BNP Paribas and Credit Suisse are in danger of having criminal charges brought against them by US and state prosecutors over helping US citizens evade taxes, a report has said.

BNP Paribas and Credit Suisse are in danger of having criminal charges brought against them by US and state prosecutors over helping US citizens evade taxes, Bloomberg has reported, citing an unnamed source.

Separately, BNP has today said that it might be hit with a US fine that is "far in excess" of the $1.1 billion provision it set aside last year to cover litigation costs linked to potential breaches of US sanctions.

"The discussions that took place during the first quarter of 2014 concerning U.S. dollar payments involving countries subject to U.S. sanctions demonstrate that a high degree of uncertainty exists as to the nature and amount of penalties that the U.S. authorities could impose on the Bank following completion of the ongoing process: there is the possibility that the amount of the fines could be far in excess of the amount of the provision," BNP said in its first quarter earnings release.

The report said that Zurich-listed Credit Suisse has been the target since 2011 of a US criminal probe into whether it helped Americans evade taxes. BNP Paribas has been the subject of a federal probe into possible violations of sanctions barring business with prohibited countries, the report said.

Prosecuting the companies would break with a past practice of brokering settlements with large banks that are considered integral to the financial system. Previous probes have been resolved through so-called non-prosecution and deferred-prosecution agreements, which have been criticised by U.S. senators for failing to hold banks accountable for breaking the law, the report said.

The US Justice Department’s tax division and prosecutors in Alexandria, Virginia, are leading the tax probe of Credit Suisse. Manhattan US Attorney Preet Bharara, Manhattan District Attorney Cyrus Vance Jr and David O’Neil, the head of the Justice Department’s criminal division in Washington, are working together in the BNP Paribas investigation, the report’s source was quoted as saying.

The report said both banks have declined to comment on the investigation; Credit Suisse has previously said it is cooperating with the DoJ probe.

Swiss and other banks have been in the cross-hairs of US authorities in recent years. The most prominent case to date has been that of UBS, which in 2009 settled criminal and civil charges that it aided US tax evaders. In another case, Wegelin, Switzerland’s oldest bank, was shut down in the US and its remaining Swiss operations were folded into a new structure after being charged in the US with aiding tax dodgers.

Last August, the Swiss and US governments signed an accord under which Swiss banks have the option of stating whether there is a risk – or not – of them having violated US tax laws. Out of the 300-plus banks in Switzerland, around a third are said to have signed up to the accord.