MONACO, May 26 (Reuters) - The family of the late French Formula One driver Jules Bianchi are planning legal action against the sport's governing body, his former Marussia team and Bernie Ecclestone's Formula One Group, they said in a statement on Thursday.

Bianchi died in hospital last July after suffering serious head injuries in a crash at the October 2014 Japanese Grand Prix.

British firm Stewarts Law, representing the family, said the death had been avoidable and formal pre-action letters of claim had been sent this week.

"The Bianchi family are determined that this legal process should require those involved to provide answers and to take responsibility for any failings," said Stewarts partner Julian Chamberlayne.

(Reporting by Alan Baldwin, editing by Ossian Shine) ((alan.baldwin@thomsonreuters.com; +442075427933; Reuters Messaging: Reuters Messaging: alan.baldwin.reuters.com@thomsonreuters.net))