French police Tuesday carried out a dozen raids concerning state-controlled nuclear giant Areva's controversial 2007 purchase of a Canadian uranium mining company, a judicial source told AFP.
The probe focuses on the $2.5 billion (1.8 billion euro) purchase by Areva of UraMin at a height of demand for enriched uranium.
Areva was later forced to revalue its UraMin uranium mines to only 410 million euros.
Canadian media reports have suggested the sale was preceded by suspicious stock trades and France's financial prosecutor has opened a preliminary probe.
Investigators searched Areva's headquarters as well as the home of Anne Lauvergeon, the company's former chief executive who ran the firm when the sale took place, the judicial source said.
Areva declined to comment when contacted by AFP.
France's Cour de Comptes, which carries out audits of public institutions and state-controlled companies, sharply criticised the handling of the purchase of UraMin.
A 2012 French parliamentary report concluded there were no fraudulent dealings in the UraMin purchase, but that it was poorly managed.