A female police employee has been killed in a knife attack at a police station south-west of Paris.
Anti-terror prosecutors have taken over the inquiry, and the killing is being treated as a possible terrorist attack.
The attacker, who reportedly came to France from Tunisia several years ago, was shot dead by police.
President Emmanuel Macron led tributes to the 49-year-old victim, and said France would never give in to "Islamist terrorism".
What do we know about the attack?
The stabbing took place in the secure entrance to the police station in the commuter town of Rambouillet at 14:20 (12:20 GMT).
Witnesses said the attacker had been seen walking around while on his mobile phone outside the police station and seized his chance to go in as the woman - an unarmed administrative officer - went through the security doors.
He reportedly lunged at the officer, stabbing her in the neck. Her colleagues then opened fire on him.
Anti-terrorism prosecutors said they took over the investigation because of the way the attack had unfolded, remarks made by the attacker and the fact that he targeted a police official.
Sources close to the inquiry told media outlets that the man had shouted "Allahu Akbar" (God is greatest) during the attack.
Officials said the attacker, 36, was not previously known to security agencies. Local outlet BFMTV reported that he had lived in the country illegally before obtaining a residency card, which was due to expire later this year.
Three people were arrested following the attack, according to reports. A judicial source told AFP news agency they were part of the suspect's "entourage".
What has the reaction been?
In a Twitter post following the attack, Mr Macron said the victim's name was Stéphanie. "The nation is by the side of her family, her colleagues and security forces," he wrote.
Her full name has not been released, but local media reports describe her as a mother of two.
Prime Minister Jean Castex and Interior Minister Gérald Darmanin went straight to the scene, in the large Yvelines area to the west of the capital.
Mr Castex said the country had lost an "everyday heroine" and condemned what he described as a "barbaric act of boundless cruelty".
"Our determination to combat terrorism in all its forms is as resolute as ever," he told reporters.
Valérie Pécresse, president of the Paris region, said the attack had been against a "symbol of France". The police, she said, were "the face of France".
Far-right leader Marine Le Pen - seen as the strongest challenger to Mr Macron in next year's presidential election - tweeted condemnation of Friday's attack before details of the suspect's identity had been made public.
"The same horrors come one after another, the same infinite sadness as we think about the relatives and the colleagues of this female police employee who has been killed, the same type of person guilty of this barbarity, the same Islamist motives," she wrote.
British Foreign Secretary Dominic Raab also reacted to the attack on Twitter.
"We stand with our French friends and allies following tragic news of a female police officer killed by a terrorist in Rambouillet while doing her job," he wrote.
In his comments on Friday, Mr Castex noted that the Yvelines area had been targeted before, including in 2016 when two members of the police force were fatally stabbed at their home.
In October 2020 the militant Islamist murder of teacher Samuel Paty in Yvelines led to national outrage, as he was attacked after an online campaign that began with false claims from a 13-year-old girl at his school.
Deadly attacks on French police
January 2015: Two police officers were among those killed in the attack at the offices of satirical magazine Charlie Hebdo. A third was killed in a related attack the following day.
June 2016: A police commander and his partner, also a police official, were stabbed to death at their home west of Paris by a man claiming allegiance to the Islamic State (IS) group. The attacker was killed in a police assault on the house.
April 2017: A French policeman was killed by a jihadist on the Champs Elysées in Paris. Two other officers were wounded in the attack. The suspect was shot dead by security forces, and a note defending IS was found near his body.
March 2018: A gunman who pledged allegiance to IS militants launched a series of attacks in southern France, killing four people including a policeman who traded places with a captive. He also opened fire on a group of police officers out jogging, wounding one. The suspect was shot dead by police.
October 2019: A police computer operator stabbed four of his colleagues to death at the Paris police headquarters, before being shot dead. Anti-terror prosecutors said he adhered to a radical version of Islam..