The Swiss attorney general's office (OAG) said in a statement on Wednesday that it had denied a Russian request for mutual judicial assistance in the case of Andrei Borodin and had lifted a freeze on his assets in place since 2014.
The order affected around 20 bank accounts in the wealthy Alpine nation containing around 300 million Swiss francs ($310 million, 265 million euros), according to Swiss public broadcaster SRF.
An OAG spokeswoman confirmed the report.
Borodin, 50, has been facing fraud allegations in Russia since 2011 when he fled the country to London, where he has since been granted asylum.
Switzerland's top prosecution authority also opened an investigation into his activities in July 2011, and agreed in 2014 to a Russian request to block his assets in the country.
But in 2015, the Swiss probe was shuttered and authorities in the country began examining the validity of agreeing to provide judicial assistance to Russia in the case.
"The OAG decided in May 2017 that the Russian request for mutual judicial assistance was inadmissable and to unblock the sequestered assets," the office said in its statement.
It stressed though that the decision applied only to Borodin's case "and not to the general cooperation" with Russian prosecutors.
Russia has also meanwhile recently refused to provide full judicial cooperation to Switzerland.
The OAG last month dropped an investigation into former Russian agriculture minister Elena Skrynnik for suspected money laundering, citing Moscow's "incomplete execution" of the requested judicial assistance in the case.