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.

French detectives are continuing to search for fugitives suspected to have been involved in the Paris massacres, as details of how police foiled the terrorists’ operations have begun to unfold.

Security forces dramatically ended a three-day terror spree around Paris, killing the two al Qaida-linked brothers who staged a murderous rampage at a satirical magazine, and an associate who seized a kosher supermarket to try to help them escape.

French President Francois Hollande has called on the country to “remain vigilant” as the hostage crisis which started at the Charlie Hebdo magazine massacre came to a bloody end with the loss of at least 20 lives.