A teacher has been killed and two people have been seriously injured in a knife attack at a school in France, officials say.
Interior Minister Gérald Darmanin said the attack happened at the Gambetta high school in the northern city of Arras at about 11:00 local time.
The attacker has been arrested and is now in custody. According to witnesses, he shouted "Allahu Akbar", or "God is greatest", during the attack.
The person killed was a French language teacher. Those injured were another teacher and a security guard.
The man, described as being in his 20s, is of Chechen origin and known to the security services for his involvement with radical Islam, according to police.
French media reports say he was a former pupil at the school.
The French anti-terror prosecutor's office says it has opened an investigation following the attack for "murder in connection with a terrorist enterprise" and "attempted murder in connection with a terrorist enterprise".
News channel BFMTV has reported that the brother of the attacker has also been apprehended by police.
Police say the situation is now under control.
French President Emmanuel Macron will visit the school later on Friday, while the National Assembly in Paris has suspended its session in solidarity with the victims.
The attack comes amid rising tensions in France's sizeable Muslim and Jewish communities due to the conflict between Israel and Hamas.
However, police have said there is nothing to indicate a link with the Middle East.
The attack comes nearly three years since the murder and beheading of another teacher, Samuel Paty, at his school outside Paris.
The perpetrator of that attack, 18-year-old Abdullakh Anzorov, a Russian Muslim refugee, was shot dead by police shortly afterwards.