A French official says a teenager detained following the killing of an 85-year-old priest by a pair of jihadi attackers in northwest France has been released.

An official with the Paris prosecutor's office said investigators questioning the 16-year-old found evidence of regular visits to jihadi sites and of "incitement to terrorism," but that the minor's case had been transmitted to prosecutors in the nearby city of Rouen who cover the region.

She spoke on condition of anonymity as she was not allowed to be named publicly. Judicial authorities in Rouen did not immediately return a message seeking comment.

A Syrian refugee and a cousin of one of the two attackers remain in custody following the attack in the town of Saint-Etienne-du-Rouvray.