SAINT-ETIENNE-DU-ROUVRAY: Muslims and Christians joined in Friday prayer 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 civilization" or "humanity."

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

The killing Tuesday of the 85-year-old Rev. Jacques Hamel as he celebrated morning Mass sent shockwaves around France, and deeply touched many among the nation's 5 million Muslims.

The Islamic State group claimed responsibility for the attack, as well as the attack in Nice, where 84 people were killed by a man who plowed his truck down a seaside promenade on Bastille Day.

The head of the main Muslim umbrella group, Anouar Kbibech, who attended Friday's gathering, reiterated a call for Muslims to visit churches on Sunday to show solidarity with Christians as they pray. But one imam made a rare direct strike at the killers who claimed to act in the name of Allah.

"You have the wrong civilization because you are not a part of civilization. You have the wrong humanity because you are not a part of humanity," said Abdelatif Hmitou. "You have the wrong idea about us (Muslims) and we won't forgive you for this."

"How," he asked, addressing the extremists, "may the idea reach your mind that we might loathe those who helped us ... to pray to Allah in this town? How could you think that, mister killer? Mister criminal?"

He was referring to the help by the St. Therese church adjacent to the mosque that sold the plot to the Muslims for a symbolic sum so they could build a house of worship. The St. Etienne church where the attack occurred has been sealed shut.

The two 19-year-old attackers were killed by police as they left St. Etienne church, where they had held two nuns and an elderly couple hostage as they slit the priest's throat. A third nun escaped and gave the alert.

Three people were being held Friday for questioning in the attack, including a Syrian refugee, a judicial official said on Friday.

The Syrian was detained on Thursday in the Allier region of central France because a photocopy of his passport was found at the home of one of the attackers, Adel Kermiche, according to the official, who was not authorized to speak publicly about the investigation.

Also being held was a cousin of Kermiche's accomplice, Abdel-Malik Nabil Petitjean, on suspicion he was aware of the attack plan based on information culled from social networks, the judicial official said. A 16-year-old arrested just after the attack remained in custody.

Two members of Petitjean's family, a sister and her companion, were released after questioning, the official said.

How Kermiche, from Normandy, concocted the attack plot with Petitjean, from Aix-les-Bain in the Alpes of eastern France, remained unclear.

What is known is that he arrived in Kermiche's town just three days earlier, apparently staying at his home, according to the judicial official.

Kermiche wore a tracking bracelet after arrests with false ID's trying to go to Syria but had four hours a day of freedom. Petitjean had no record.

Petitjean's identity was made public only on Thursday based on DNA tests. It became clear that anti-terrorist officials came close twice to identifying him as a threat. In one instance, four days before the attack, an alert with a photo of him went out to police with a note he may be planning an attack — but the photo had no name to match the face. He was spotted in Turkey in June but French authorities were alerted too late and he quickly returned to France.

Outside the mosque a sign read: "Mosque in mourning."

The Rev. Pierre Belhache, in charge of relations with the Muslim community, affirmed to the Muslim and Christian faithful that "we won't let anyone divide us.

"It is so rich to have these differences but still be together."