According to Consob, in 2010 Bollore bought shares in Premafin, a Ligresti family holding company that owned the struggling Italian insurer.

The watchdog said Bollore pushed the value of Premafin shares to artificially high levels in 2010 when he bought the stock through his holding companies Financière de l'Odet and Financiere du Perguet between September 22 and October 22.

Bollore said in a statement the acquisition of Premafin shares had been conducted legally and that his Financiere de l'Odet holding company will appeal this decision.

The transactions occurred at a time when rival French insurer Groupama was ready to agree with the Ligresti group to subscribe to Fondiaria's capital increase, and that Bollore's actions were designed to facilitate the deal, a source familiar with the matter said.

Fondiaria ran into financial difficulty in 2009 and by 2010 was forced to consider asset sales and cash calls to prop up its balance sheet.

Consob said Premafin shares rose 25.96 percent in the month during which Bollore carried out the purchases compared to the 3.68 percent rise in the Italian all-shares index, Consob said.

Tax police arrested Salvatore Ligresti, his children and former executives of Fondiaria in July as part of an ongoing probe into false accounting and market manipulation.

(Reporting by Stephen Jewkes and Lionel Laurent; Editing by Louise Heavens)