PARIS • French police have detained a former flatmate of a man arrested over an attack with a meat cleaver that left two wounded outside the former offices of satirical weekly Charlie Hebdo, a judicial source said yesterday.

Police also late Friday released another man who was close to the scene of the attack in Paris but who was confirmed to have been a witness who had "chased the assailant", the source said.

Seven people are being held in connection with the attack, which came three weeks into the trial of suspected accomplices in the 2015 massacre of the newspaper's staff.

They include the "main perpetrator", who was arrested not far from the scene, prosecutors said.

France's PNAT specialist anti-terror prosecution office on Friday said it had opened a probe into charges of "attempted murder related to a terrorist enterprise" against him as well as "conspiracy with terrorists".

According to PNAT head Jean-Francois Ricard, the suspect was an 18-year-old man.

Initial indications were that he was born in Pakistan. French Interior Minister Gerald Darmanin on Friday said the attack was "clearly an act of Islamist terrorism".

The suspect has confessed to the attack, sources close to the investigation said yesterday.

The man "takes responsibility for his action which he places in the context of the republication of cartoons" of Prophet Mohammed in Charlie Hebdo, one of the sources said.

Charlie Hebdo has angered many Muslims around the world by publishing cartoons of Prophet Mohammed over the years and, in a defiant gesture, reprinted some of the caricatures ahead of the trial.

Twelve people, including some of France's most celebrated cartoonists, were killed in the attack on Charlie Hebdo by Islamist gunmen on Jan 7, 2015.

Paris police said two people were "critically wounded" in Friday's attack near the paper's former offices in the French capital's 11th district. Charlie Hebdo's new address is kept secret.

A source close to the investigation confirmed to Agence France-Presse on Friday that a large meat cleaver found near the scene was used by the attacker.

The judicial source said yesterday that a man was taken in for questioning who had been a flatmate of the main suspect when he was living in social housing in the Val-d'Oise department north of Paris.

Five more people arrested in the Paris suburb of Pantin during a search of a property linked to the main suspect were also being held, a judicial source said late on Friday.

The Premieres Lignes news production agency said the wounded were its employees - a man and a woman taking a cigarette break outside.

The company specialises in investigative reports and produces the prize-winning Cash Investigation programme.

The stabbing came during the trial of 14 alleged accomplices of Said and Cherif Kouachi, the brothers who were perpetrators of the 2015 attack that was claimed by a branch of Al-Qaeda.

A female police officer was killed a day later, followed the next day by the killing of four men in a hostage-taking at a Jewish supermarket by gunman Amedy Coulibaly.

France has experienced a wave of attacks by Islamist militants in the past few years.

Bombings and shootings in November 2015 at the Bataclan theatre and sites around Paris killed 130 people, and in July 2016 an Islamist militant drove a truck through a crowd celebrating Bastille Day in Nice, killing 86.

AGENCE FRANCE-PRESSE, REUTERS