A 21-year-old man arrested on suspicion of stabbing a French soldier in the neck in Paris was flagged to French intelligence months ago over fears that he had been radicalised, it was claimed.
Alexandre D, as the French suspect has been called, was arrested at a friend's flat in Yvelines, just west of Paris.
Investigators are seeking to determine whether the Paris attack last weekend was inspired by the Islamist murder of a British serviceman in London.
Contrary to earlier claims by the Interior Ministry and Paris prosecutor, police sources told Le Monde French intelligence was recently warned that the suspect, who converted to Islam about three years ago, was "becoming increasingly radical".
The warning came in a note written by the police intelligence unit of the Yvelines area where Alexandre D was arrested.