France's anti-terrorist unit is now investigating the Paris knife attack in which four police officers died, the Paris prosecutor's office told Euronews.

The officers were killed at their Paris headquarters before the suspect was shot dead.

The attacker, a 45-year-old man, had been working as an administrative assistant in the IT department of the Paris police since 2003, French Interior Minister Christophe Castaner said.

"He had never shown any behavioural difficulty and today went on this murderous path", Castaner said.

Government spokesperson Sibeth Ndiaye said there was "no indication of possible radicalisation."

In an interview with Franceinfo, she said converting to Islam was not an "automatic sign of radicalisation."

"We mourn the death of four civil servants from two services in the Paris police force", the Paris prosecutor said in a press conference. "Three men and one woman, three of them worked as police officers and one as an administrative assistant, have been killed."

Another victim was still in hospital and is recovering.

The Paris police said that it had been "afflicted by a terrible drama" and thanked president Emmanuel Macron, the PM Edouard Philippe and the Interior Minister for their support.

The Interior Minister said he sent "thoughts to the families of the victims" and guaranteed his "full support" to the entire Paris police staff.

He praised the work of "all police officers in France, who work every day to prevent crime such as the one that happened today in this very place."

An investigation into "murder and attempted murder on people in a position of public authority" has been opened by the Paris prosecutor's office, the prosecutor said.

"Paris mourns this afternoon after this horrific attack at the [police headquarters]. The death toll is high, several police officers lost their lives. On my behalf and on the behalf of Parisians, my first thoughts go to the family and relatives of victims," Anne Hidalgo, the Mayor of Paris, tweeted.

"All our thoughts are with the victims and their families," French Justice Minister Nicole Belloubet said in an address in the country's parliament, l'Assemblée Nationale. "In these painful and tragic circumstances, we send our full support to employees and civil servants of the Paris police."

The incident comes after thousands of police officers took part in an "anger march" on Wednesday to demand better working conditions and respond to high suicide rates amongst police forces.

This article is being updated as events unfold.

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