Two assailants slit the throat of an 84-year-old priest at a church in northern France on Tuesday in a hostage-taking drama that has shocked the country.
The attack in the Normandy town of Saint-Etienne-du-Rouvray came as France was still reeling from a massacre in the French Riviera city of Nice claimed by Daesh.
The motivations for the hostage-taking were not yet clear, but the Paris prosecutor's office said the case was being handled by anti-terrorism prosecutors.
Five people were inside the church in the when it came under attack, interior ministry spokesman Pierre Henry Brandet said.
He said the church was surrounded by France's anti-gang brigade the BRI, which specialises in kidnappings, and that "the two assailants came out and were killed by police".
The priest died after having his throat slit, sources close to the investigation told AFP. The archbishop of the nearby city of Rouen, Dominique Lebrun, named him as 84-year-old Jacques Hamel.
French Prime Minister Manuel Valls expressed his horror at what he called "a barbaric attack on a church".
"The whole of France and all Catholics are wounded. We will stand together," he wrote on Twitter.
Pope Francis voiced his "pain and horror" at the hostage-taking, according to the Vatican.
The archbishop of Rouen, Dominique Lebrun, urged all non-believers to join those of the church in "calling to God".
"The Catholic Church can take up no other weapons that prayer and fraternity between men," he said in a statement.
The Nice attack was the third major strike on France in 18 months and was claimed by the Daesh.
Two attacks in Germany claimed by Daesh since then have also increased jitters in Europe.
After the attack in Nice, France extended a state of emergency giving police extra powers to carry out searches and place people under house arrest for another six months until January.
It was the fourth time the security measures have been extended since Daesh militants struck Paris in November, killing 130 people at restaurants, a concert hall and the national stadium.
Bitter political feud
The Nice massacre has triggered by a bitter political spat over alleged security failings, with the government accused of not doing enough to protect the population.
French far-right National Front leader Marine Le Pen wrote on Twitter that the "modus operandi obviously makes us fear a new attack from terrorist."
Valls had warned earlier in the week that the country will face more attacks as its struggles to handle extremists returning from jihad in the Middle East and those radicalised at home by devouring propaganda on the internet.
France has been concerned about the threat against churches ever since a foiled plot against in the Paris suburb of Villejuif in April last year.
Sid Ahmed Ghlam, a 24-year-old Algerian IT student, was arrested in Paris on suspicion of killing a woman who was found shot dead in the passenger seat of her car, and of planning an attack on a church.
Prosecutors say they found documents about Al-Qaeda and Daesh at his home, and that he had been in touch with a suspected militants in Syria about an attack on a church.