Intelligence agencies have accessed the encrypted private messages of France's most notorious Isil propagandist, prompting almost a dozen arrests in a month – mostly teenagers – according to reports.

Rachid Kassim, a 29-year old former child carer has become France's new public enemy number one after being linked to at least two jihadist murders and a string of plots.

Despite this, he has come under severe criticism from Isil sympathisers for the "amateurism" of his online terror tips.

Kassim has 317 followers on Telegram, an encrypted messaging service, from which he runs a "public jihadist channel" and offers advice on how to carry out attacks in private chats.

He is suspected of "remote-controlling" from his Syria base the failed attempt to blow up a Peugeot packed with gas near Notre Dame cathedral in Paris ten days ago.