In a Belgian town where dozens of young people have departed to wage jihad in Syria, the bloody attacks in Paris were the mosque director’s worst nightmare.

Just days after the deadly assaults in the French capital, anti-Muslim graffiti went up at the soccer stadium in this hardscrabble Brussels suburb where marginalized Muslim youths have proved susceptible to quick radicalization. Far-right Flemish nationalist parties warned of sweeping new security measures aimed at Muslim communities. And after modest success in containing surging Islamist extremism, mosque director Mimoun Aquichouch worried anew about a setback.

The wave of terror in and around Paris last week that left 17 people plus the perpetrators dead has French leaders deeming the tragedy their nation’s 9/11. But the reverberations extend far beyond France as divisions in Europe widen between alienated young Muslims and security officials wary of extremist threats.

Here in Belgium, police carried out anti-terrorist raids Thursday across the country, including near Vilvoorde, thwarting what they said was an imminent attack from suspects who had just returned from Syria. In the town of Verviers, 75 miles east of Brussels, they killed two suspects and injured a third.

Of all the European countries confronting the anger and alienation behind the eruption of violence in France last week, nowhere is the fight as intense as in Belgium, which has become Europe’s most fertile recruiting ground for jihadists to join the battle to establish an Islamic caliphate in Syria and Iraq. The conflict in those countries is a cauldron for extremist groups that increasingly threaten to extend their violence into Europe. More than 350 Belgians have gone to Syria, security officials say, the highest number per capita among European countries and a shock for a nation whose population of 11 million is smaller than Ohio’s.

Korans in Arabic and French are on display inside the Annasr Mosque in Vilvoorde, Belgium. (Virginie Nguyen Hoang /For The Washington Post)

Tensions spiked after the Paris attacks, and members of Muslim communities in Belgium say they feel under siege again. Their children are taunted at school, anti-Muslim graffiti has been scrawled near mosques, and lawmakers are debating rules that could strip citizenship from Belgians who take up arms in Syria.

But the anger may be cutting both ways. Four Brussels bookstores on Wednesday received threats telling them not to sell copies of the new issue of Charlie Hebdo, the satirical newsweekly targeted in the attack last week that left 10 staffers and two police officers dead. The latest issue of the newspaper features a cartoon of a crying prophet Muhammad on the cover. Many Muslims say any depiction of the prophet is offensive.

Some Muslim leaders here are warning that Belgian proposals to crack down on the threat of homegrown Islamist violence may actually worsen the problem.

Meanwhile, Interior Minister Jan Jambon on Wednesday proposed making it easier to deploy the Belgian army domestically and to give authorities the power to strip citizens of their nationality should they go to fight abroad.

The country was confronting similar threats even before the Paris attacks. A French national named Mehdi Nemmouche is accused in a gun attack at a Brussels Jewish museum in May that killed four. Nemmouche had previously fought in Syria.

So far, no Belgian citizen has carried out a domestic attack.

“I cross my fingers and say that happily, nothing has happened here in Belgium,” said Aquichouch, who immigrated from Morocco as a child and is the head of the only mosque in Vilvoorde, a struggling industrial suburb of 41,000 just six miles north of the European Union’s glimmering steel-and-glass buildings in Brussels. Security officials believe 28 of Vilvoorde’s residents have gone to fight in Syria.

The Kasap Mehmet butchery near the Annasr Mosque on in Vilvoorde. (Virginie Nguyen Hoang /For The Washington Post)

But Aquichouch said that he could not swear that Belgium will continue to be spared a domestic attack.

“We’ve seen that young people here are easily manipulated,” he said. “It’s easy to convince people of this radicalism. They don’t go to school and don’t really know their religion.”

Security officials say that Belgium’s pipeline to Syria was built by a group called Sharia4Belgium, and one of its leaders was a charismatic Antwerp street preacher and sometime petty criminal named Fouad Belkacem. The flow started in early 2012. Belgian authorities started a crackdown last year, and 46 people associated with the group are on trial. Many of those who went to Syria had long criminal records; some may have gone to escape prosecution, security officials say.

The extremist recruiters had particular success in Flemish parts of Belgium, especially in Antwerp, where far-right Flemish nationalist parties have taken a hard stand against immigrants. The city banned the wearing of head scarves in 2009, and in 2011 a ban on full-face veils in public took effect in Belgium, although Muslim leaders say just a few women in the country wore them. France has a similar ban.

Some of the fiercest anger toward Belgium’s mainstream society comes from native-born descendants of Muslim immigrants who say they are treated as foreigners in the country of their birth.

“They see your hair is black — okay, then you’re in trouble,” said Hadji Akber, 45, the owner of a fast-food restaurant on a central Vilvoorde square that combines the kebabs of his native Turkey with the frites of his adopted homeland. He refused to give his full name, out of safety concerns.

“All four of my children were born here,” he said. “My son doesn’t want to go to Turkey, because he gets bored. But he’ll always be a bit foreign here.”

Those divisions are swiftly widening. Two days after the attack on Charlie Hebdo in Paris, graffiti went up on the wall of the Vilvoorde soccer stadium popular among Muslim youths. The message read, “All Muslims have to leave Europe,” and was signed “Charlie Hebdo,” said Vilvoorde Mayor Hans Bonte. He deployed police officers to remove the graffiti as quickly as possible, he said.

“There is a radicalization effect on both sides of the societal spectrum,” Bonte said.

Critics say that the new proposals to combat extremism are focused too much on fighting it after its development and too little on its root causes.

“It is a kind of speedy reaction, a knee-jerk reaction to respond to public anxiety and pressure,” said Rik Coolsaet, a Ghent University professor who has advised the Belgian government on counterterrorism policy.

The anger has even touched grammar school classrooms. Brahim Botaleb, 38, who was shopping for religious music at a bookshop in a heavily Muslim part of central Brussels this week, said that his 9-year-old son was being taunted at school by children chanting, “Charlie, Charlie,” a reference to Charlie Hebdo.

Some Brussels residents say they are retrenching.

“We were going to go to Paris this weekend, but my husband canceled it,” said Ouaidia Khamal, 39, whose pink hijab framed her face behind the counter at her discount shop in central Brussels.

“He said with a face like his, he can’t go over there right now,” she said. “People have asked me, ‘Why don’t you go back to your country?’ But I was born here.”