The murder of a policewoman near Paris was an attack on the nation, French Prime Minister Jean Castex said, as extremism cast a dark shadow over France once more.
She was stabbed to death by a Tunisian man on Friday in a suspected terrorist attack at a police station south-west of Paris.
The attacker, identified by AFP as Jamel Gorchene, 36, was fatally wounded when officers opened fire on him at the station in Rambouillet, a wealthy commuter town 60 kilometres from Paris.
"Once again, the Republic has been attacked," Mr Castex said on Saturday.
"Once again, the French state has been threatened. We will not let this go by."
French President Emmanuel Macron said on Twitter that "in our fight against Islamist terrorism, we will never give in", identifying the murdered woman as Stephanie.
"The nation is by the side of her family, her colleagues and security forces," he said.
Paris regional president Valerie Pecresse said terrorist motives could not be ruled out and the antiterrorism prosecutor's office said it was opening an investigation.
A cousin, who identified himself as Noureddine, said Gorchene was "a quiet person, not particularly pious".
A brother-in-law said Gorchene recently returned home to Tunisia where he spent two weeks.
His parents live in M'saken, a town not far from the city of Sousse.
The attack occurred in the secure entrance area of the station at about 12.20pm GMT, a police source said.
It is understood that the victim, 49, was an administrative employee at the station and was repeatedly stabbed in the neck.
According to reports, she was attacked when she returned to the station after changing a parking disc on her car.
"The National Police are once again bereaved by a despicable attack," the SCPN, which represents the national police force, tweeted.
"[We] support the family and loved ones of our colleague.
"All police officers of all ranks and bodies know that to serve is to risk your life in the face of fanaticism and extremists."
French Interior Minister Gerald Darmanin confirmed the victim was an officer.
"A police officer was the victim of a knife attack at the Rambouillet police station," he tweeted.
Politician Aurore Berge said the incident was an "attack on France".
"Whenever our law enforcement agencies are attacked, it is France that is attacked," she said.
"Rambouillet is a town that is not at all used to being subjected to violence.
"This reminds us that our law enforcement agencies put their lives at risk every morning when they go to work."
The incident follows the fatal stabbing of four people at Paris police headquarters in 2019 and comes six months after an Islamist teenager beheaded schoolteacher Samuel Paty in the same administrative department of France.
Earlier this year, parliamentarians in France's lower house backed a bill that President Macron said was designed to rid the country of extremism and protect French values.
It will implement stricter monitoring of the country's mosques and schools after a wave of extremist attacks.