French prosecutors have opened an investigation into the assets owned by Russian oligarchs, a legal source said on Monday.
The probe is expected to look into possible money laundering and corruption.
The investigation, first reported by the Parisien newspaper, comes after anti-graft group Transparency International filed a legal complaint against oligarchs in France in May.
France has frozen Russian-owned assets worth billions of euros since the Kremlin's invasion of Ukraine in February, including luxury yachts, ski chalets and property.
The country's Mediterranean coast, high-end ski resorts and Parisian real estate market have long been favored destinations for Russian cash for investment and leisure.
"The ambitions of the sanctions regime against Russia and the first asset seizures are running into difficulties in identifying the assets owned by sanctioned individuals," Transparency International France said in a statement last month.
"In France, as elsewhere, the hunt for goods owned by oligarchs and others close to the Russian regime is at a standstill," it added as it filed its legal case.
The French government has said it faces serious difficulties in identifying and seizing assets that are often owned by overseas shell companies.
Transparency International said it had "drawn up an inventory of real estate assets in France of several oligarchs and people close to the Russian regime."
It said it possessed evidence of how the money used to pay for them came from illicit sources.
European Union countries have frozen assets worth 13.8 billion euros ($14.1 billion) linked to sanctioned Russian and Belarusian individuals, according to figures from July 12.
The EU has so far adopted six sanction packages against Russia, including a ban on most Russian oil imports that was approved in early June.
The French probe will be led by specialised investigators at the Central Office for the Repression of Major Financial Crime, part of the National Financial Prosecutors' Office.