A French prosecutor has opened an investigation into whether Swiss refiner Petroplus illegally withdrew funds from its French unit before filing for insolvency.

The "fraudulent insolvency" probe, opened by the Nanterre public prosecutor, on Wednesday saw its financial police unit search the subsidiary's headquarters in Paris as well as Deutsche Bank, where the firm holds its bank accounts.

Petroplus said it refuted all allegations of fraudulent bankruptcy in France.

The prosecutor's office, which had access to book-keeping documents of the French subsidiary when it was put under judicial protection, is looking closely at the transfer of €100 million euros (SFr120 million), a spokeswoman at the prosecuting office said on Thursday.

"The prosecutor's office had access to documents which need to be checked, and more specifically those related to questionable financial transfers," she added. But the prosecutor may struggle to prove the criminal charge of "bankruptcy by embezzlement" because Petroplus is insolvent in France and in the rest of Europe.  

Zug-based Petroplus filed for insolvency on Tuesday, putting over 2,000 jobs across Europe at risk, after it defaulted on $1.75 billion (SFr1.61 billion) of debt. The group owns five refineries including one in Cressier, canton Neuchâtel, which shut down this week.          

Europe's largest independent refiner by capacity has been teetering since its lenders restricted credit late last year, a victim of thin refining margins and high debt.  

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