French investigators were on Saturday questioning three people linked to a Tunisian man who stabbed a police employee to death near Paris in a suspected Islamist attack.
The murder at a police station in Rambouillet, a commuter town about 60 kilometers (40 miles) from Paris, revived the trauma of a spate of deadly attacks last year.
The victim was a 49-year-old woman named as Stephanie M., a police administrative assistant and mother-of-two, who was stabbed twice in the throat at the entrance of the station.
Her 36-year-old attacker named as Jamel G., who had not been known to police or intelligence services, was shot and fatally wounded by an officer at the scene.
President Emmanuel Macron, who was out of the country on a visit to Chad, tweeted that France would never give in to "Islamist terrorism".
The latest violence targeting police is likely to focus attention further on the danger of extremism in France and wider concerns about security a year ahead of a presidential election.
Prime Minister Jean Castex said he would hold a meeting in Paris with ministers and security officials after the killing.
National anti-terrorism prosecutors have opened a terror investigation.
Security stepped up
Jamel G's father and two other people were taken into custody on Friday, and questioning was continuing on Saturday as police delve into his background, contacts and possible motives.
The assailant had arrived in France illegally in 2009 but had since obtained residency papers, a police source said. He had just moved to Rambouillet.
Far-right leader Marine Le Pen immediately questioned why the attacker had been able to settle in the country, and hit back at recent criticism about police brutality in France.
"We need to get back to reason: supporting our police, expelling illegal immigrants and eradicating Islamism," she wrote on Twitter.
Polls show her running close to Macron in next year's election, though experts warn that surveys conducted so far ahead and during a pandemic should be interpreted with caution.
About 30 police officers wearing balaclavas raided the suspect's home in Rambouillet on Friday, AFP reporters said.
At the same time police in the Paris region searched the home of the person who had sheltered Jamel G. when he first arrived in France, sources close to the inquiry said.
Interior Minister Gerald Darmanin, who also visited officers in Rambouillet, said security would be stepped up at stations nationwide.
