Five top magistrates are looking into the 26 "targets" suspected of involvement in money-laundering schemes that passed cash through Panama, the Seychelles, Switzerland, Hong Kong and Singapore in an effort to dodge French tax authorities, according to Le Monde newspaper.
The investigators are part of an elite white-collar crime unit set up following revelations that then finance minister Jérôme Cahuzac had dodged tax through a secret Swiss bank account.
The targets are either wealthy individuals believed to have hidden millions in shell companies or banks, lawyers and other intermediaries believed to have helped them.
Tax officials chase 415 individuals
On Tuesday Le Monde revealed that French tax authorities have launched investigations into 415 individuals suspected of large-scale tax evasion due to the Panama Papers revelations about the activites of the Mossack Fonseca legal practice.
The figure was whittled down from more than 500 by removing people who had died, accounts that belonged to a household already on the list and people who had come forward voluntarily after the scandal hit the headlines in April 2016.
Panamanian authorities are reported to be cooperating, with the chief prosecutor attending European judicial cooperation meeting on Monday and Tuesday, partly due to the threat of being placed on a blacklist of tax havens that is due to be drawn up at a G20 meeting in Germany in July.
Setback for Swissleaks investigation
Despite having netted billions of euros in unpaid taxes since its establishment, the anti-corruption unit is suffering from insufficient resources, lack of recognition from the upper levels of the police and political pressures, according to a letter signed by 25 of its agents sent to the chief of police, the Mediapart website revealed last month.
Tax fraud investigators received a blow from Switzerland on Wednesday when a court ruled that the authorities must not cooperate with the Swissleaks investigation.
The federal tax administration at first gave a positive response to a French request for help in a probe targeting a couple accused of tax-dodging.
But the court ordered the authorities not to help the inquiry because the suspects were identified by files stolen by former HSBC employee Hervé Falciani.
"There is no disputing the reprehensible origins of the Falciani data," the ruling said, recalling that a Swiss court in 2015 sentenced him in absentia to five years in prison.
The French-Italian national alleges that HSBC helped more than 120,000 people avoid taxes.
Following the court ruling, France committed to not using any information linked to him when seeking further legal assistance from Switzerland.