France was on high alert on Saturday as thousands of troops were deployed on the streets after the fatal stabbing of a teacher and the Louvre museum was evacuated following a security threat.
Friday's attack took place at a high school in the northeastern town of Arras, home to large Jewish and Muslim populations.
On Saturday, amid fears that the conflict between Israel and Hamas could lead to violence in foreign capitals, France announced it would deploy up to 7,000 soldiers under the highest warning level.
In Paris, a spokeswoman for the Louvre, the largest museum in the world, said it had "received a written message stating that there was a risk to the museum and its visitors".
Alarms rang out through the vast museum in central Paris overlooking the Seine River when the evacuation was announced, and in the underground shopping center beneath its signature pyramid.
Police cordoned off the monument from all sides, and the underground access, as tourists and other visitors streamed out. Videos posted online showed people leaving, some hurriedly and some stopping to take photos, others apparently confused about what was happening.
Mohammed Moguchkov, who is in his twenties and of Chechen origin, was arrested at the high school where he attacked several people on Friday, killing one and wounding several others.
He was already on a French national register known as “Fiche S” as a potential security threat, a police source told AFP, and under electronic and physical surveillance by France's domestic intelligence agency, the DGSI.
Authorities have suggested a probable link to the continuing violence in Gaza, with President Emmanuel Macron denouncing the incident as what he called an act of “Islamist terrorism”.
The deployment of the soldiers from Operation Sentinelle will be completed by Monday evening, according to the Elysee presidential palace.
Sentinelle is a French military operation with 10,000 soldiers and 4,700 police and gendarmes deployed since the aftermath of the January 2015 attacks to protect parts of the country deemed sensitive from terrorism.
“This school was struck by the barbarity of Islamist terrorism,” Mr Macron said after visiting the scene, adding that the victim had “probably saved many lives” with his courage in blocking the attacker.
Mr Macron said an attempted attack in another region had been foiled by security forces.
According to the interior ministry, the president was referring to the arrest of a “radicalised” man who was arrested leaving a prayer hall in the Yvelines region of Paris for carrying a prohibited weapon.
Interior Minister Gerald Darmanin later said there was “probably a link between what's happening in the Middle East and this incident” in Arras.
France upped its alert level to the highest position following a crunch security meeting chaired by Mr Macron on Friday.
A total of 10 people were in custody on Saturday, a police source said.
In addition to the suspect, several members of his family were arrested “for the purposes of the investigation”, including one of his brothers and his sister, other police sources said.
The national anti-terrorist prosecutor announced that it has opened an investigation.
The victim, a French language teacher at Gambetta high school, was stabbed in the throat and chest.
Among those wounded were a school security guard who was stabbed multiple times and is fighting for his life, and a teacher in a less serious condition, the source added.
A cleaner was also hurt, according to anti-terror prosecutor Jean-Francois Ricard.
No pupils at the school were hurt, another police source said.
The attack comes almost three years to the day after the October 16, 2020 beheading of teacher Samuel Paty, also by a Chechen, near his school in a Paris suburb.
“Three years after the assassination of Samuel Paty, terrorism has struck a school again and in a context that we all know,” Mr Macron said.
Police say Moguchkov's 17-year-old brother was detained close to another school.
The pupils and teachers were confined to the school premises before being allowed out in the afternoon.
A large security cordon was set up around the school where parents had gathered, and police, firefighters and emergency services were deployed.
Martin Dousseau, a philosophy teacher who witnessed the attack, described a moment of panic during break-time, when schoolchildren found themselves face-to-face with the armed man.
“He attacked canteen staff. I wanted to go down to intervene, he turned to me, chased me and asked me if I was a history and geography teacher,” Mr Dousseau said.
“We barricaded ourselves in, then the police arrived and immobilised him.”
France has suffered a series of attacks by Islamist extremists since 2015 including the suicide and gun attacks in November 2015, claimed by the Islamic State group, on targets in Paris where 130 people were killed.
There has been a relative lull in recent years, though officials have warned that the threat remains.
Mr Macron said in an address to the nation on Thursday that 582 religious and cultural facilities in France were receiving stepped-up police protection after the attack by Hamas on Israel.
Speaking in Arras, he reaffirmed his message from that address for the French to “stand shoulder to shoulder” and “stay united”.
French Education Minister Gabriel Attal said in a message to regional education officials security should be reinforced at schools “without delay”.
Mr Darmanin on Thursday had banned pro-Palestinian demonstrations in France until further notice, on the grounds they “are likely to generate disturbances to public order”.
In defiance of his order, several hundred people gathered in Paris and other French cities on Thursday shouting pro-Palestinian and anti-Israeli slogans.
Police in Paris used tear gas to disperse the protesters, and said they had arrested 10 out of around 3,000 people present.