A 45-year-old IT assistant at the police headquarters in central Paris went on a knife rampage inside the building on Thursday, killing three police officers and an administrative worker before he was shot dead, French officials said.

The officials declined to say what the motive was for the attack, which took place at lunch-time, and that they were still trying to understand if there was a terrorism link.

But sources close to the police were quoted by French media as saying that the attacker had a grievance with his managers.

Jean-Marc Bailleul, a police union leader, described the incident as criminal rather than an act of terror.

“It was a moment of madness” Bailleul told BFM TV.

The area around the police headquarters, which is close to Notre-Dame Cathedral, was sealed off and a metro station was shut for security reasons as the attack unfolded.

The dead, three men and a woman, included three police officials and a police administrative assistant, according to Paris prosecutor Remy Heitz. 

A fifth person who was wounded in the incident is undergoing surgery.

Heitz said police were searching the attacker’s home, and that anti-terrorist investigators were evaluating what had happened, for any terrorist links.

French Interior Minister Christophe Castaner said the attacker was known to his colleagues and had worked for some time in the IT department.

“He had never presented any behavioural issues, he had never presented the slightest cause for alarm before going on his deadly rampage today,” Castaner said.

A police official and member of the collective “Police up in Anger”, which lobbies for better conditions for officers, was quoted by franceinfo radio as saying the assailant had experienced issues with his supervisor.

“I know there were tensions between him and his direct supervisor. I do not think this is a terrorist act,” Christophe Crepin told franceinfo. 

On Wednesday, thousands of police marched through the streets of Paris, protesting at poor working conditions they say have led to dozens of suicides among their ranks this year.

According to the latest numbers given by police unions, 52 police officers have committed suicide so far in 2019.

- Reuters