The suspect’s father, a couple who had provided him with an address for mail and other administration, and another cousin were also being questioned, Mr Ricard said.

French authorities have detained a fourth person as anti-terrorism investigators question three others after a police official was fatally stabbed at a police station outside Paris.

French prosecutors have opened a terrorism investigation into the fatal stabbing of a French police officer inside her police station near the historic Rambouillet chateau outside Paris.