By George Wright & Gem O'ReillyBBC News
AFPPolice say the situation is now under controlA teacher has been killed and two people seriously injured in a knife attack at a school in France.
The attack happened at Gambetta high school in the northern city of Arras at about 11:00 local time (09:00 GMT).
The attacker has been arrested and is now in custody.
Witnesses say he shouted "Allahu Akbar", or "God is greatest", during the attack. Visiting the school, President Emmanuel Macron condemned the "barbarity of Islamist terrorism".
Mr Macron called on French people to stay "united" in the face of the attack, to "not give in to terror or let anything divide us".
He said police had averted another attempted attack in another part of France.
The man killed was a French language teacher. Those injured were another teacher and a security guard.
Mr Macron said the teacher had "come forward to protect others and had without doubt saved many lives".
The attacker, named as 20-year-old Russian national Mohamed Mogouchkov, is of Chechen origin and known to the security services for his involvement with Islamist extremism, according to police.
As a former pupil at the school, he alarmed teachers with his views.
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.
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.
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