Paris Knife Attack: The assailant, Mickael Harpon, was eventually shot dead by police (File Photo)

A staffer at Paris police headquarters who stabbed four colleagues to death in a frenzied attack adhered to "a radical vision of Islam", an anti-terror prosecutor said Saturday.

The 45-year-old computer expert had been in contact with members of Salafism, an ultra-conservative branch of Sunni Islam, and defended "atrocities committed in the name of that religion", Jean-Francois Ricard told reporters.

Three police officers and an administrative worker -- three men and one woman -- died in the 30-minute attack on Thursday at the police headquarters, a stone's throw from the Notre-Dame cathedral in the historic heart of Paris.

The assailant, named as Mickael Harpon, was eventually shot dead by police.

The incident sent shock waves through an embattled French police force already complaining of low morale.

On the morning of his "extremely violent" attack, Harpon bought two knives, a 33-centimetre long kitchen knife and an oyster knife which he kept hidden, Ricard said.

Shortly before, he had exchanged 33 text messages with his wife who was still being held by police on Saturday.

The messages exclusively concerned religion, and the attacker ended the conversation with "Allahu Akbar" ("God is greatest") and told her to "follow our beloved prophet Mohammed and meditate on the Koran", according to the prosecutor.

Harpon, who supported the Charlie Hebdo attacks in 2015, had changed his attire in recent months, shunning "all Western clothes in favour of traditional garments to visit the mosque", Ricard added.

He also wished to no longer "have certain kinds of contact with women".

'True Drama'

French President Emmanuel Macron, who has described the attack as a "true drama", will lead tributes to the victims on Tuesday, the Elysee announced on Saturday.

Sources at the Paris prosecutor's office said on Friday the case had been passed to the anti-terrorist prosecutor's office PNAT after early enquiries suggested that the attacker, a convert to Islam, could have become radicalised.

Harpon, born on the French overseas territory of Martinique in the Caribbean, converted to Islam about 10 years ago, the prosecutor said.

He had no police record but was investigated for domestic violence in 2009.

Sources said he had worked in a section of the police service dedicated to collecting information on jihadist radicalisation.

French police have been a recurring target of jihadist groups, such as Islamic State, behind a wave of attacks since 2015 -- from large synchronised assaults to isolated knife and gun attacks.

In June, a parliamentary report on radicalisation within the public services spoke of 30 suspected cases out of the 150,000 police officers and 130,000 gendarmes in France.