SAINT-ETIENNE-DUROUVRAY, France (AP) — Two attackers slit the throat of an 85-year-old priest celebrating Mass in a French church, killing him and gravely injuring one of the few worshippers present before being shot to death by police.

A nun who escaped said she saw the attackers take a video of themselves and “give a sermon in Arabic” around the altar.

The Islamic State group claimed responsibility for the attack, the first inside a church in the West.

Police rescued three people inside the church – including a second nun – in the small northwestern town of Saint-Etiennedu Rouvray, said Interior Ministry spokesman Pierre- Henry Brandet.

A regional Muslim leader said one of the two attackers was known to police, and a police official said he had tried to go to Syria. The official, who spoke on condition of anonymity to reveal details of the investigation, said the man was under police supervision and wore an electronic bracelet to monitor his movements.

A statement published by the Islamic State-affiliated Amaq news agency said the attack was carried out by “two soldiers of the Islamic State” who acted in response to calls to target nations in the U.S.-led coalition fighting IS in Iraq and Syria.

The statement echoed claims in other recent attacks in France and neighboring Germany. It repeated its threat to Western “crusaders.”

A special intervention force carried out a search for possible explosives in or around the church.

“The investigations are ongoing. There are still unknowns,” Brandet said. “There are dogs, explosive detectors and bomb disposal services” at the church outside the city of Rouen, the capital of France’s

Normandy region.

A nun who was in the church said the Rev.

Jacques Hamel was forced to the ground before his throat was slit. The nun, identified as Sister Danielle, told BFM television: “They forced him to his knees. He wanted to defend himself. And that’s when the tragedy happened.”

She said the attackers recorded themselves.

“They did a sort of sermon around the altar, in Arabic. It’s a horror,” she said.

Dominique Lebrun, the archbishop of Rouen, confirmed Hamel’s death.

“I cry out to God, with all men of good will. And I invite all non-believers to unite with this cry,” Lebrun wrote in a statement from Krakow, Poland. “The Catholic Church has no other arms besides prayer and fraternity between men.”

The priest “was always ready to help,” said Rouen diocese official Philippe Maheut. He said Hamel had been at the church for the past decade.

French President Francois Hollande, arriving on the scene, called it a “vile terrorist attack” and one more sign that France is at war with the Islamic State group.