A witness to the murder of the priest slain by Islamist militants in France was forced to record the brutal incident, he has revealed after speaking publicly for the first time.

Guy Coponet told the Famille Chretienne that the two attackers, Adel Kermiche and Abdel-Malik Petitjean, forced him to hold a camera and film them slitting the throat of 86-year-old Father Jacques Hamel.

"They even checked the quality of the image and that I wasn't trembling too much," Coponet said. "I had to film the assassination of my friend Father Jacques!"

The assailants were hoping to use the video as Islamist propaganda, "which would allow them to earn their fame as a 'martyr' of Allah", Coponet said.

Both attackers were shot dead at the scene by police.

The incident occurred on July 26 and Copenet was himself stabbed a number of times in the arm, back and throat.

The emergency doctor who treated him said it was a miracle he survived. "There was a divine hand on you because no shots have hit a vital organ," the medic said. "But it really was not far away... It's like a miracle."

"The Lord allowed me to survive to show his mercy," Coponet said. While he was lying on the ground, blood pouring from his neck, he prayed to God: "Father I abandon myself to You, do with me what you please... I commend my spirit into your hands."

He continued: "I was convinced that I would die, but... I was calm. I have never been so serene. Completely at peace. I had no remorse, only love... In fact, it was a moment of great happiness."

Copenet and his wife Janine were at the parish church at Saint-Etienne-du-Rouvray, near Rouen, to attend a mass led by Father Jacques.

Pope Francis has signalled that he is preparing to canonise the priest, who could be made a saint without needing miracles because he died a Christian martyr.

His last words were "Satan, get out of here, get out, Satan", Sister Danielle, who was also a witness to the killing, told Famille Chretienne.

But she added that Father Jacques was not claiming that his killers were possessed, but that "Satan was at work in a powerful way".

"Father Jacques wanted to exorcise this evil," she said. "Satan does not like the Eucharist."

Sister Danielle also said that Kermiche had asked one of her fellow nuns: "Are you afraid of dying?" The nun replied: "No... Because I believe in God and I know I'll be happy."

The jihadist reportedly replied: "I also believe in God and I am not afraid of death."

The Copenets say they are able to forgive their assailants, even for the murder of their beloved priest.

"We are just saying, 'Father, forgive them, they know not what they do'," the couple said.