In a statement, prosecutors said they had also issued arrest warrants for 14 associates of Micalizzi, some of whom are already in jail. They did not give further details.

A legal source told Reuters Micalizzi was arrested as part of an investigation into a 600 million euro (485.7 million pounds) fraud that has allegedly damaged a range of companies including gas operator Snam, Pirelli, JP Morgan, UBI Banca and UBS.

The companies were not immediately available to comment. It was not possible to reach Micalizzi for comment.

Micalizzi was the chief executive of the collapsed London-based Dynamic Decisions Capital Management fund. The fund, which had mainly invested in highly illiquid bonds, was liquidated after racking up losses amounting to more than 85 percent of its value.

Britain's Financial Services Authority (FSA) banned him in May 2012, saying he was not "fit and proper" to perform any role in regulated financial services.

(Reporting by Manuela D'Alessandro; additional reporting by Milan bureau; writing by Lisa Jucca; editing by Tom Pfeiffer)