French officials eye social media’s role in promoting unrest.

Thousands of protesters are expected to pour onto city streets across France again on Saturday, a now-weekly expression of national grievance that has led to clashes between protesters and the police, and kept the country on edge.

Adding to those fears: Halloween, which also falls on Saturday. The French authorities, citing calls on social media for people to revolt and encouraging them to wear masks and costumes, warned that the risk of a new outbreak of violence was high.

Huge demonstrations last Saturday did not descend into the lawlessness that erupted the week before, in part because of a heavy security force, which will be marshaled again. In Paris, the authorities moved the route for marchers to the city’s eastern periphery, as they did previously, drawing outrage and fruitless legal challenges from organizers.

France’s interior minister, Laurent Nuñez, warned on Thursday that it could be a “day with a very high risk to public order.” He promised to deploy 70,000 police officers, matching the numbers on Oct. 24. That operation helped keep a lid on outbreaks of arson and looting, although there were clashes as the police tried to disperse the crowds in the evening.

There is ample fuel for a repeat of those combustible scenes. Students, who are returning to school on Monday after a two-week break, were not mollified by the government’s initial response to their demands. The Education Ministry agreed to cap some class sizes, offer low-interest loans to rebuild school buildings and phase out an unpopular online college admissions platform.

The students vowed to go on protesting. Their two-month-old movement has grown to include university students, public workers and veterans of the “yellow vest” movement that convulsed France from 2018 to 2020.

While tensions could rise during the day, the authorities said they were most worried about trouble breaking out after nightfall.

“We are seeing numerous calls to gather coming from the far left, the radicalized extreme left, and from certain radicalized ‘yellow vests’ websites, which are urging people to attend rallies or public gatherings starting at 8 p.m. in many cities across France,” Mr. Nuñez said at a news conference.

Some of the messages were violent, Mr. Nuñez said, calling for “revolution” and “insurrection.” Those gatherings will be forbidden, and any attempt to gather in spite of the ban will lead to arrests, he said.

Demonstrators have been encouraged on social media to turn up wearing Halloween costumes. Mr. Nuñez warned it was a criminal offense to conceal one’s face during a demonstration in which public order is disrupted.

Social media: French officials are increasingly concerned about the role played by social media in attracting people and inciting them to violent behavior. Speculation that the government considered temporarily suspending several popular sites drew a denial from President Emmanuel Macron himself. Read more ›

Far-right activists: While the government has blamed far-left activists for much of the mayhem, officials confirmed that bands of young men with links to the far right have also infiltrated the demonstrations. They use the pretext of protecting shop owners but often end up in clashes with far-left groups.

Widening movement: The nationwide unrest in France began with a handful of student demonstrations at high schools in suburban Paris last month. Read more ›

Giulia Imbert contributed reporting.

As France prepares for another round of protests, officials have grown increasingly concerned about the role played by social media in attracting people to demonstrations and inciting them to violent behavior.

Speculation that the government considered temporarily suspending several popular sites drew a denial from President Emmanuel Macron himself.

But in an interview on YouTube, Mr. Macron said that social media platforms would be required “to remove illegal content, and to be very vigilant about the use of certain features to prevent them from being misused by people who want to engage in looting or other such activities.”

That followed a report by a left-leaning online news site that Prime Minister Sébastien Lecornu had sent a letter to leading telecommunications operators, asking them to be prepared to block Snapchat, TikTok and Instagram. Mr. Lecornu’s office declined to comment on the authenticity of the letter.

Of the four reported recipients, one did not respond to questions and two declined to comment. A spokesman for the fourth, Orange, the only one in which the state is a shareholder, declined to confirm that a letter was received but said that “like any other operator, we are required to comply with the obligations legally imposed on us by the competent authorities, in accordance with applicable law.”

The nationwide unrest in France began with a handful of student demonstrations at high schools in suburban Paris last month.

Now, in cities across the country, antigovernment marchers are protesting expensive living conditions, high fuel prices and conditions in schools. Using the unrest as a smoke screen for vandalism, rioters and looters have also joined in.

With the protests in their second month, the police have arrested thousands, and politicians are divided over how to respond.

Here is a breakdown of what has happened.

Soon after returning from the summer break, students at a high school in the working class Parisian suburb of Créteil staged a protest, according to videos posted to social media on Sept. 18. The high schoolers objected to inadequate resources and high workloads.

Within days, students elsewhere around Paris initiated similar demonstrations. At schools in the capital’s poorest suburbs, students blocked entrances to protest crumbling infrastructure, overcrowded classrooms and what they say are flaws in the admissions system for higher education.

By Sept. 29, the unrest had spread to around 400 schools around the country, according to rally organizers.

The union of high school students said the blockades were a protest against a “lack of teachers and staff, dilapidated schools, overcrowded schedules and classrooms.”

Students barricaded the entrances to some schools with obstacles including e-bikes, while others threw projectiles and set fire to trash cans.

The French education minister, Édouard Geffray, said that some of the students’ demands were “legitimate” but condemned the confrontational nature of their protests. He said that students had chased teachers and targeted school principals with firework-launching tubes.

By the end of September, nearly 80 people had been injured, and the authorities had detained more than 440, including many minors.

Within days, the number of schools engulfed in the protests had doubled. According to the Interior Ministry, by Oct. 2, they had spread to more than 1,000 schools across France, including 220 that were blockaded. University students also began taking part.

Around this time, the authorities said that the protests were mutating from legitimate expressions of educational grievances into something more dangerous, accusing people of shooting mortar-style fireworks, burning public buildings and looting.

By Oct. 2, nearly 400 police officers and over 230 school employees and students had been injured. The number of arrests climbed to 3,000.

The actions widened in October to encompass labor unions, parents and other activists, as different grievances converged into a mass protest.

On Oct. 6, around 256,000 people marched through Paris and 40 other French cities, according to the Interior Ministry. A union of high school students said protesters had occupied some 1,800 high schools.

The protests were mostly peaceful, but a fire was ignited in Lyon, and police officers used tear gas, including in Paris. The total number of arrested rose to 6,000, the authorities said. A major union of French judges and prosecutors and a human rights group accused the police of using disproportionate force, including against children as young as 14.

Two days later, on Oct. 8, smaller demonstrations were staged throughout the country, rallying around 71,500 people. The following week, the Interior Ministry said that 160,000 people joined marches on Oct. 13 across France.

More than half a million people joined 110 antigovernment marches throughout France on Oct. 17, according to an official estimate. A major union, the C.G.T., put the number even higher, at 800,000. Using either count, it was the largest day of protest since the demonstrations began in September.

Many of the marchers were peaceful, but some were not. Around the country, rioters vandalized around 1,500 shops, the authorities said. In Paris, where over 100,000 people marched peacefully, a few hundred rioters faced off against officers. According to the police, the rioters burned cars and smashed storefronts.

In the large town of Limoges, in central France, rioters set fire to the 19th-century City Hall. In a moment captured on video, the building’s spire collapsed in flames.