An investigation has been opened after one of the hostages in the January attacks around Paris accused some television and radio stations of having put his life in danger and sued them, the city’s prosecutors’ office said.

A huge security operation is being prepared ahead of unity marches in France, as the hunt for a fugitive linked to the Paris massacres took a new twist.

A businessman taken hostage by the Charlie Hebdo killers has described how he kept a colleague from their clutches in an act of heroism which helped police capture the fugitives.