“We have been made aware from sources close to the investigation that the accounts have been frozen,” William Browder, the founder of Hermitage Capital investment fund, told AFP from London.

His comments came after the US finance magazine Barron’s reported on Thursday that Swiss prosecutors had frozen accounts at Credit Suisse bank as an “emergency” measure, citing sources.

Russia is investigating Western investment fund Hermitage Capital for tax evasion in a complex long-running case during which company lawyer Sergei Magnitsky died in jail in 2009 from untreated illnesses while awaiting trial.

The fund claims it was a victim of a tax swindle in which officials stole identities of companies belonging to it and claimed back hundreds of millions of dollars in tax refunds.

The claims centre around the former head of a Moscow tax office who now works in a different state-controlled firm.

Browder said he had information that “dozens of accounts” had been frozen after the fund submitted criminal complaints about money at Credit Suisse belonging to the husband of the former tax official, Olga Stepanova.

“Based on information coming out of Switzerland, we believe these accounts were frozen,” Browder said.

Dozens of Russian officials have been banned from travelling to the United States and Europe over the Magnitsky case.

On Wednesday, a Moscow court approved a request from police investigators to issue an arrest warrant for a Russian executive in the fund, Ivan Cherkasov, who is working in London.

Russian investigators have said they believed that Cherkasov had failed to pay taxes on some two billion rubles ($71.95 million at Friday’s exchange rate) in company profits in 2006 in a complex legal case.