Four police officers were killed and one injured in a knife attack in Paris last week, prompting French prosecutors to launch a terror investigation into the matter.

France's interior minister Christophe Castaner has warned that the terrorist risk in France remains 'high' to 'very high' in the wake of the deadly attack that resulted in the deaths of four police officers.

Castaner also admitted that the killing of the officers could have been prevented, but that opportunity had been missed.

Addressing opposition calls for him to resign, the minister stressed that he would not be stepping down.

The official also underlined that since 2003, the police had thwarted 59 terrorist attacks, including three attempts since the beginning of this year.

Last Thursday, a software engineer went on a stabbing spree injuring law enforcement officers with a knife at his workplace in the centre of the French capital.

The assailant was identified as 45-year-old Michael Harpon. A total of five people, including the attacker, were killed in the incident.

France’s national anti-terrorism prosecutor, Jean-Francois Ricard, later said that Harpon was a radicalised Islamist. The incident prompted French prosecutors to open a terror investigation into the deadly attack.

Moreover, Prime Minister Edouard Philippe said on Sunday, that French special services would undergo thorough evaluations.