NANTERRE, France (AP) — Young rioters clashed with police and looted stores Friday in a fourth day of violence in France triggered by the deadly police shooting of a teen, piling more pressure on President Emmanuel Macron after he appealed to parents to keep children off the streets and blamed social media for fuelling unrest.

Police said 270 people had been arrested by midnight nationwide.

Despite repeated government appeals for calm and stiffer policing, Friday saw brazen daylight violence, too. An Apple store was looted in the eastern city of Strasbourg, where police fired tear gas, and the windows of a fast-food outlet were smashed in a Paris-area shopping mall, where officers repelled people trying to break into a shuttered store, authorities said.

The southern port city of Marseille, initially spared the violence that broke out first in the Paris region, was experiencing its second night of upheaval. Even before nightfall, young people hurled projectiles, set fires, and looted shops, police said. They made almost 90 arrests. On Friday evening, looters broke into a Marseille gun shop and made off with weapons, and a man was later arrested with a hunting rifle, police said. The previous night, two off-duty officers suffered serious injuries, including one who was stabbed, when they were set upon by about 20 people, police said.

Authorities in the city of Lyon reported rioters again setting fires and pelting police in the suburbs. In the city center, police made 31 arrests to stop the attempted looting of shops after an unauthorised protest against police violence that drew about 1,300 people Friday evening.

In the face of the escalating crisis that hundreds of arrests and massive police deployments have failed to quell, Macron held off on declaring a state of emergency, an option that was used in similar circumstances in 2005.

Instead, his government ratcheted up its law enforcement response. Already massively beefed-up police forces were boosted by another 5,000 officers for Friday night, increasing the number to 45,000 overall, the interior minister said. Some were called back from vacation. The minister, Gerald Darmanin, said police made 917 arrests on Thursday alone and noted their young age — 17 on average. He said more than 300 police officers and firefighters have been injured.

Darmanin also ordered a nationwide nighttime shutdown of all public buses and trams, which have been among rioters’ targets.

And he said he had delivered a warning to social networks that they can’t allow themselves to be used as channels for calls to violence.

“They were very cooperative. We’ll see tonight if they really are. We are going to give them as much information as possible” so that, in return, French authorities get the identities of people who incite violence, the minister explained.

“We will pursue every person who uses these social networks to commit violent acts,” he said. “And we will take all necessary measures if we become aware that social networks, whoever they are, don’t respect the law.”

Macron, too, zeroed in on social media platforms that have relayed dramatic images of vandalism and cars and buildings being torched, saying they are playing a “considerable role” in the violence. Singling out Snapchat and TikTok, he said they were being used to organise unrest and serving as conduits for copycat violence.

Macron said his government would work with technology companies to establish procedures for “the removal of the most sensitive content,” adding that he expected “a spirit of responsibility” from them.