French police killed the Tunisian suspect in the Friday slaying of an unarmed administrative employee at the entrance of her police station in the town of Rambouillet.

The suspect's father is among the four currently held, a judicial official said on Saturday. A couple who had housed the suspect at one point and a member of his entourage, who was detained Saturday, also were being questioned.

The victim, a National Police employee, had left the station to extend her time on a parking metre and was followed into the entry area by the attacker, who was shot to death by a police officer.

The attack jolted the French government into taking a deeper look at new steps needed to protect police officers. Interior Minister Gerald Darmanin is to present a bill shortly giving new teeth to an anti-terrorism law, the national intelligence coordinator, Laurent Nunez, said Saturday on BMFTV.

"(Police) know we have a difficult fight against Islamist terrorism ... the fight won't stop tomorrow or the next day," Darmanin said after meeting with police in the Brittany town of Quimper, which he was visiting.

French President Emmanuel Macron, meanwhile, visited the family of the victim, a 49-year-old identified only as Stephanie. She lived in Thoiry, about 30 kilometres north of Rambouillet. The president's office said he wanted "to show support and solidarity with the family ... very upset and very dignified."

The attacker, identified by authorities as Djamel G., entered France illegally in 2009 and was given residency papers in 2020, a judicial official said.

He had staked out the police station ahead of time, anti-terrorism prosecutor Jean-France Ricard said. The preparation, along with statements he said during the attack and the targeting of a police official, prompted the national anti-terrorism prosecutor's office to take over the investigation.

The 37-year-old suspect had no criminal record or record of radicalisation, French media reported.

But witnesses heard him say "Allahu akbar!" Arabic for "God is great," during the attack, said the judicial official who was not authorised to discuss the investigation publicly.

At least some in his hometown of Msaken, near the eastern coastal town of Sousse, were shocked that he could be the attacker. While authorities identify him as DJamel, he identifies himself as Jamel on Facebook.

"He is a man who belongs to an average family and he's a kind person. We grew up together," said Mohamed Ben Abdejlil , 35.

Ben Abdejlil said he had visited Jamel in Rambouillet, before his friend obtained residency papers, but had not heard from him since. Still, he said, "I was shocked by what I heard today about what he had done, unbelievable."

Infrequent Facebook and Instagram posts from accounts thought to have belonged to the suspected attacker hinted at a man who waffled over the years about his allegiances but showed no overt ties to an extremist ideology. The US-based SITE Intelligence Group initially uncovered the accounts.

The judicial official confirmed to The Associated Press that the name associated with the accounts "appears" correct, but in keeping with French practice, the official would not confirm the attacker's full name.

Jamel G.'s last post on April 18 is a prayer for a blessed Ramadan, the Muslim holy month now in progress.

Among previous attacks, three French police officers and an administrative employee were killed by a colleague in 2019 inside Paris police headquarters. A police couple was also murdered in 2016 in their home in the same region as Rambouillet.

Australian Associated Press