Muslims and Catholics joined in Friday prayers at the mosque in the Normandy town where an elderly priest was slain this week, with one imam chastising the extremists as non-Muslims who are "not part of civilisation."

Muslims came from other parts of France for the service shared with Christians.

The killing of 85-year-old Fr Jacques Hamel as he celebrated morning Mass sent shockwaves through France. ISIS claimed responsibility for the attack, as well as the July 14 truck attack in Nice, where 84 people were killed by a man who plowed his truck down a seaside promenade.