ANKARA

About 5,000 residents in France have been judged to be 'predisposed to violence' by French intelligence services, and are under surveillance, a former head of the services told radio station RTL on Friday.

 Former head of France's Central Directorate of Interior Intelligence, Bernard Squarcini said in an interview that "you have to find out what these people will do before they take action. In general, these are people who get up early and go to bed late. They are watched on a 24-hour basis."

It requires 25 people to watch a single suspect, and then you have to follow up on the people they meet, Squarcini said, adding that certain targets, therefore, had to be prioritized.

Squarcini said that more resources and legal freedom of action should be provided to intelligence forces, in order to take earlier preventive action.

French Interior Minister Bernard Cazeneuve told radio station Europe 1 on Thursday: "The Charlie Hebdo attackers were known to the police. They had previously been under surveillance. But they were not under investigation by the judiciary. Nothing suggested that they were planning a terrorist attack." 

Suspects of the attack that killed 12 people at the Charlie Hebdo offices in Paris on Wednesday, Franco-Algerian Said Kouachi, 34, and Cherif Kouachi, 32, are reported to be holding a hostage in a building northeast of Paris.

Police have surrounded the building.