A friend of one of the two men who killed a French priest in Normandy was detained only days before the attack took place, reports say.

The 17-year-old tried to travel to Syria last year with Adel Kermiche, French and Swiss media say.

The unnamed teenager was reportedly arrested in Geneva earlier this month and handed over to French authorities.

Days later, on Tuesday, his friend Kermiche went on to kill Father Jacques Hamel in his church near Rouen.