The Bank of France's banking commission also issued a formal warning to Societe Generale, one of France's biggest banks, saying that shortcomings in "hierarchical controls" over an extended period in 2007 fuelled the problem.

Societe Generale officials in Paris declined to comment on the decision, which was announced on the Bank of France website.

The bank accuses trader Jerome Kerviel of massive unauthorised trades which led to the losses. Kerviel's lawyer says his superiors were aware of his activities.