The man believed to have carried out the Paris knife attack on Friday has told police he had targeted weekly satirical magazine Charlie Hebdo, a police source has told Reuters news agency

The attack took place near the former offices of the French magazine where islamist militants gunned down employees in 2015 because of the republication of cartoons depicting Prophet Mohammad.

By midday Saturday, a total of seven people remained in custody in connection with the attack in Paris that left two people seriously injured on Friday. 

Meanwhile a suspected accomplice of the attacker was released in the early hours of Saturday morning. 

Paris police said two people were "critically wounded" in Friday's attack, which is being investigated by specialist anti-terror prosecutors. An earlier statement had said four were wounded, two seriously.

The main suspect, identified as an 18-year-old man, was detained close to the Place de la Bastille square, not far from the scene. His custody had been extended on Saturday morning, confirmed a judicial source.

Police and prosecutors said he faces possible charges of "attempted murder related to terrorism" and "conspiracy with terrorists." 

The suspected assailant was arrested a month ago for carrying a screwdriver but was not on police radar for Islamic radicalization, Interior Minister, Gérald Darmanin confirmed.

Darmanin said it was "clearly an act of Islamist terrorism" and "a new bloody attack against our country, against journalists, against this society."

A second person was also been detained in the Bastille area, a judicial source told AFP. 

In a tweet, Charlie Hebdo condemned the attack:  "This tragic episode shows us once again that fanaticism, intolerance, the origins of which will be revealed by the investigation, are still present in French society....There is no question of ceding anything."

A staff member for the Premieres Lignes news production agency said two colleagues were hurt in the attack.

"Two colleagues were smoking cigarettes in the street. I heard screams. I went to the window and saw a colleague, bloodied, being chased by a man with a machete," the employee said.

France's Prime Minister, Jean Castex said the lives of the two injured workers were not in danger and offered the governments solidarity for their families and colleagues.

Five schools in the area immediately went into lockdown with no one allowed to leave or enter.

The attack came during a trial of alleged accomplices in the January 2015 attack on the offices of Charlie Hebdo that killed 12 people.

"A serious event has taken place in Paris," prime minister Jean Castex told reporters as he headed to the crisis centre of the interior ministry.

"Four people have been wounded and it seems that two are in a serious condition."

He added the attack had taken place "in front of" Charlie Hebdo's former offices, in the 11th district of central Paris. The magazine's current address is kept secret for security reasons.

Eye-witness Mohamed Zaidi said: "I saw one or two people running but that was the way I was going, so I kept going and there at the foot of the metro I saw a machete with lots of blood and I saw people shouting, it was a bit of a panic. 

"To get to my office, I took the passageway that is right next to my work and there I saw a victim lying there, covered in blood. That's when I panicked and then people started panicking and shouting and I went to my work to warn my colleagues to lock themselves in and the police arrived at that point and asked us to stay locked up."

Trial of 14 defendants 

Some of France's most celebrated cartoonists were killed in the 2015 attack, carried out by brothers Said and Cherif Kouachi and claimed by a branch of Al Qaeda. 

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

The 14 defendants stand accused of having aided and abetted the perpetrators of the 2015 attacks, who were themselves killed in the wake of the massacres.

The magazine, defiant as ever, had marked the start of the trial by republishing hugely controversial cartoons of the prophet Mohammed that had angered Muslims around the world. Al-Qaeda then threatened Charlie Hebdo with a repeat of the 2015 massacre of its staff.

More than 100 French news outlets on Wednesday called on people to support Charlie Hebdo, taking aim against the "enemies of freedom."

Police moved the magazine's head of human resources, Marika Bret, from her home following death threats received last week.

The trial in Paris had resumed Friday after a suspect's coronavirus test came back negative. The hearing for the 14 suspects, which opened on 2 September, was postponed Thursday after Nezar Mickael Pastor Alwatik fell ill in the stand.

His lawyer Marie Dose said her client had suffered from "a lot of fever, coughing, vomiting and headaches."

He was back in the box on Friday, after the presiding judge informed defense and prosecution lawyers by SMS late Thursday that the test results allowed for the trial to go ahead.

Video editing: Riaz Jugon Video animation: Paula Harvey Video producer: Simon Ormiston