The killing of Nahel Merzouk ignited long-simmering tensions between police and young people in France's housing projects, who struggle with poverty and unemployment.

He was shot during rush hour on Tuesday morning while driving a car in Nanterre, a small town on the outskirts of Paris.

A passenger in the car has released a video on social media saying he wants to "establish the truth ... because there are a lot of lies on social media".

Saying he wants to "tell you the story from A to Z," the young man explains they borrowed the Mercedes and decided to go for a drive around Nanterre, adding: "We weren't under the influence of any alcohol or drugs."

They were driving in the bus lane when they noticed police motorbikes following them with flashing lights and stopped the car.

He says an officer approached the window of the car and told Nahel to lower it before saying: "Cut the engine or I'll shoot you."

The young man claims the officer then struck Nahel with the butt of his gun, then the second officer arrived and also hit Nahel with the butt of his weapon.

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'Don't move or I'll put a bullet in your head'

He says the first officer then put a gun to Nahel's head and said: "Don't move or I'll put a bullet in your head."

The young man alleges the second officer said: "Shoot him."

He says the first officer then stuck Nahel again with the butt of the gun, causing him to release his foot from the brake pedal and making the car move forward.

He says the second officer then fired his weapon, so Nahel put his foot on the accelerator.

'I'm shocked at what happened in front of me'

"I saw him in pain, he trembled," he says. "We hit a barrier.

"I was afraid. I got out of the vehicle. And I ran away. I thought they might shoot me. So I ran."

He adds: "I'm shocked at what happened in front of me. To my friend."

Officer's use of weapon not legally justified, prosecutor says

The officer who shot and killed Nahel has asked his family for forgiveness.

Nanterre public prosecutor Pascal Prache said officers tried to pull the teenager over because he looked so young and was driving a Mercedes with Polish licence plates in a bus lane.

He allegedly drove through a red light to avoid being stopped and then got stuck in traffic.

The officer said he feared he and his colleague or someone else could be hit by the car as Nahel attempted to flee, according to the prosecutor.

Mr Prache said his initial investigation had led him to conclude the officer's use of his weapon was not legally justified.

The officer has been put under formal investigation over voluntary homicide and is being held in prison in preventive detention. Under the French legal system, being placed under formal investigation is akin to being charged in the UK.