'France is losing a generation to hate'

Mr Valls said: "The terror threat will last for years. We will have to spend much more on security." Other speakers shared Mr Valls's pessimism, with many saying that very little was being done to deradicalise France's Islamists. Programmes to forge dialogue with extremists and fight the inciters were just beginning, they said.

Mr Uzan said: "All radicals, from the far-right, antisemites to Islamists are working together. It's not just a bunch of bloggers writing things they believe in. Spreading hatred is a lucrative business. Those inciting online have many teams of well-paid professionals, experts who have been developing new methods for 20 years.

"We're only just starting to understand what inciters are doing and how to stop them. We believe that contradicting their theories is not the answer because they can always reply with other arguments. The method we think is effective is to show to people who they are, what they're doing and how."

Several experts said that radical recruiters were targeting 14-year-olds because they are vulnerable, easy to manipulate, and critical of society and their families.

"Most terrorists who struck France and Belgium were young adults when they carried out their attacks, but were recruited much earlier," said psychoanalyst Hélène L'Heuillet.

Guillaume Denoix de Saint Marc, whose father was killed in an aircraft bombing in 1989 and who works on deradicalisation, said:

"Teachers are lost. They have no idea what to do when they talk to these children." He added that it was impossible to deradicalise an extremist.

"They have to go along that path on their own. We can give them information and help them but we can't deradicalise them. It just doesn't work that way."