At least one police officer was shot dead and two other officers injured when a gunman opened fire in Paris' Champs Elysees on Thursday night.
The gunman was shot dead by security forces at the scene.
French authorities have identified the attacker but not released his name.
ISIS has claimed responsibility for the attack, which comes ahead of France's Presidential Elections on Sunday.
Paris: Shooting at Champs-Elysees shopping boulevard
Shotgun, knives found in gunman's car
Local media reported that police found a pump-action shotgun and knives in the gunman's car.
The unnamed attacker is reportedly 39 years old and lived in Paris suburbs. He was the focus of an anti-terror investigation.
Three family members of the gunman have reportedly been taken into police custody.
Another man allegedly linked to the attack has turned himself in to Belgian police.
French media identify gunman as Karim Cheurfi
French media have identified the gunman as Karim Cheurfi, but this hasn't been officially confirmed.
In the early 2000s, Cheurfi had been convicted of attempted murder for shooting two police officers. He served several years in prison.
He was recently identified by intelligence services as a potential Islamist radical.
However, ISIS has named the attacker as Abu-Yusuf al-Baljiki on its Amaq news outlet.
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22 Apr 2017
Champs Elysees shooting: Gunman was held earlier over suspicion
He was arrested and his home raided in February after he was overheard talking about killing police, but the hunting knives and masks recovered weren't considered sufficient proof of murderous intent.
No links with Islamist militants was found then, either.
He had earlier been jailed four times.