Attackers Who Killed Priest at French Church Were Teens Who 'Claimed Allegiance to ISIS'

— -- The attackers who stabbed and killed an elderly priest at a church in France this morning after claiming allegiance to ISIS were both teenagers, the Paris prosecutor said.

One attacker was identified as 19-year-old Adel Kermiche, who had tried to go to Syria twice and was known to anti-terrorism forces, the Paris prosecutor said.

Kermiche was under house arrest with a tracking bracelet when he carried out the deadly attack in Normandy with an unidentified second attacker.

In March 2015, Kermiche was found in Germany trying to use his brother’s ID to get to Syria, the prosecutor said. Kermiche was returned to France, arrested and put under house arrest.

Two months later he left home again, and an international arrest warrant was issued. He was found and arrested in Turkey. He flew there using a cousin’s ID, the prosecutor said.

He was returned and jailed, and in March 2016 an anti-terrorism judge put him back under house arrest with a bracelet. He had to stay with his family and was allowed out of the house only at certain times of day. He was expected to report once a week to the police and could not leave the region, the prosecutor said.

The attackers were “terrorists who claimed allegiance to ISIS,” French President François Hollande said earlier today.

ISIS’ Amaq news agency said that the attack was carried about by “soldiers of the Islamic State” and that the attack was “in response to calls for attacks on the Crusader alliance.”

The attack began when two people armed with knives entered a church in the city of Rouen, about 80 miles outside Paris, during morning Mass and took hostage six people — a priest, nuns and parishioners.

One nun escaped and alerted police, who tried to start negotiations, the Paris prosecutor said.

The priest, who was 86 years old, was killed from stabs to the neck and torso, the Paris prosecutor said.

An 86-year-old worshipper was also stabbed, the Paris prosecutor said. The worshipper’s condition was not immediately disclosed.

One of the attackers had three knives, a handgun and a fake, aluminum-wrapped suicide vest, the Paris prosecutor said. The other attacker had a backpack with a fake explosive.

When the attackers went outside, they were shouting “Allahu akhbar,” the Paris prosecutor said, at which point they were “neutralized.” Both attackers were killed outside the church, said a representative for the French interior minister.

The priest was identified by the archbishop as Jacques Hamel.

People took to Twitter to mourn the slain priest. One woman said she was baptized by him; another Twitter user said the priest recently christened her young cousin.

A nun who was in the church told French TV the priest was forced to his knees before he was attacked with the knife, The Associated Press reported.

“He wanted to defend himself,” said the nun, identified as Sister Danielle. “He was a great priest.”

The mayor’s office in St.-Etienne-du-Rouvray said the church had not received specific threats.

One person was detained for questioning in connection with the attack, a spokeswoman for the Paris prosecutor’s office said.

Hollande said he spoke to the family of the killed priest. Hollande praised the police for their quick response, which he said saved lives.

The mayor’s office in St.-Etienne-du-Rouvray said in a statement, “A barbaric act was committed in our town this morning. Our priest was assassinated, and a hostage was severely injured. We are devastated. This emotion goes beyond our town. It plunges our entire country in a deep pain, only days after the attack in Nice. The mayor and the entire municipality calls upon you all that are attached to the values of our republic to come and express your emotion, pain and indignation.”

A registry of condolences has been set up, and residents can leave flowers or candles on the steps of City Hall, the mayor’s office said, adding that flags will be flown at half-staff throughout the municipality.

Town officials are expected to meet tonight to discuss a public ceremony for the victims, the mayor’s office said.

Hollande said that the terrorists want to “divide us” and that the attack targeted not just Catholics but all of France. He said terrorists will stop at nothing, adding, “We must wage war against Daesh [ISIS].”

He called Pope Francis today and expressed the French people’s pain, telling him that when a priest is attacked, the entire nation is hurt. Hollande said everything would be done to protect churches and places of faith. He also spoke of France’s role in the defense of Christians in the Middle East and said that in such painful and grueling circumstances, he hoped harmony triumphs over hate.

The Vatican called the situation an act of “absurd violence” and said Francis strongly condemned “every form of hate” and prayed for the victims.

The White House’s National Security Council spokesman, Ned Price, said the U.S. offers condolences “to the family and friends of the murdered priest, Father Jacques Hamel.”

“Our thoughts and prayers are with the other victims of the attack as well as the parishioners and community members,” Price said.

“France and the United States share a commitment to protecting religious liberty for those of all faiths, and today’s violence will not shake that commitment. We commend French law enforcement for their quick and decisive response and stand ready to assist the French authorities in their investigation,” he said.

ABC News’ Louise Dewast, Kirit Radia and Hugo Leenhardt contributed to this report.