The Belgian teenager was determined to join the jihadist fight in Syria — so much so that, after his nation’s authorities rolled up an alleged militant cell Friday, he was speeding up his plans to depart for war.

Belgian security services came for him at his high school later in the day. Now he is sitting in detention, waiting for a judge to determine his fate, authorities say. It was just the latest example of Belgium’s alarming problem with radicalization, which has put the nation of 11 million at the forefront of Europe’s battle against homegrown terrorism influenced by faraway Islamist warriors.

Europeans have been shocked by 10 days of violent drama this month that underlined the threat in their midst. It started when two brothers claiming ties to al-Qaeda killed 12 people at a Paris satirical newsweekly and continued last week with the arrests of dozens of people accused of plotting terror in France, Belgium and Germany.

More than 350 Belgians have gone to Syria to fight, the highest number per capita of any European country. Like other European nations, Belgium is experiencing the consequences of what critics call decades of ineffectiveness in integrating immigrants, including many Muslims. But the country faces particular challenges because it has long been starkly divided itself, with bitter rivalries between a Dutch-speaking north and a French-speaking south. That has hurt the coherence of the government’s response and exacerbated the difficulties that immigrants have had fitting in.

Belgian troops were deployed across the nation Saturday to protect potential terrorist targets, a rare measure that came after authorities arrested 13 people in nationwide raids that began Thursday aimed at forestalling an attack. Greek media reported Saturday that authorities there had detained four more people connected to that conspiracy. Belgian investigators later said they did not believe there was a link between the alleged extremists in the two countries.

Hundreds of troops are deployed in Belgium, after a series of raids and arrests on an Islamist group that authorities say was planning to attack police. (Reuters)

Many frustrated members of Belgium’s Muslim community say that the best long-term protection for the nation would come from improved efforts to integrate vulnerable immigrant groups, not from added security measures.

They point to such steps as a 2012 ban on the full-face veil as increasing alienation.

“It’s okay that society has problems with radicalization. This is correct,” said Mohamed Achaibi, vice president of the Muslim Executive of Belgium, the official umbrella organization for the country’s religious community. “But why does society have problems with Muslim symbols? Why does society have problems with mosques in regions or in cities?”

Sharia4Belgium

Prosecutors say members of the cell broken up in recent days were planning to kill police officers and possibly were within hours of carrying out an attack. Authorities said they discovered heavy weaponry, explosives, phony police uniforms and walkie-talkies belonging to the group in a safe house near the German border. Two of the suspects were killed after they opened fire on police moving in on them.

Belgian authorities were already pursuing a major case against members of a group called Sharia4Belgium, in the country’s largest-ever terrorism trial. Prosecutors allege that 46 people worked as members of a terror organization to funnel fighters to Syria. A verdict in that case was pushed to next month in the wake of the Paris shootings.

Sharia4Belgium is a key factor in Belgium’s emergence as a source of radical fighters headed for the Middle East. Analysts say it created a logistical glide path for would-be jihadists who went from Belgium’s rolling countryside to the arid deserts of Syria. Even many who did not go with the group’s assistance were inspired by friends who had traveled with the help of Sharia4Belgium and stayed in touch through Facebook and other social networks. A charismatic street preacher named Fouad Belkacem spearheaded the group’s efforts, prosecutors say.

“They were using Facebook, using pictures of the villa they were living in” in Syria, said E.U. Counterterrorism Coordinator Gilles de Kerchove, who said he blamed Sharia4Belgium for the high rate at which Belgian citizens had departed for Syria. “They tried to advertise it was the ultimate place with swimming pools and easy living.”

Authorities believe about 100 of the Belgians who have gone to fight in Syria have since returned home. Some of them were among the group of alleged plotters arrested in recent days.

But the problem of disaffected Muslim youth in Belgium goes well beyond one underground group.

Muslims make up 6 percent of Belgian society, and some say they have faced long-standing challenges within the country’s majority Catholic culture — even those whose families have lived here for generations. Joblessness is far higher among Belgians with immigrant backgrounds, offering scant hope for the future.

Sharia4Belgium highlighted legal measures such as the 2012 ban on the full-face veil as examples of the society’s intolerance for Muslims. Religious communities have also run into difficulties in being allowed to carry out ritual sacrifices of animals during important annual holidays.

Few imams speak Dutch

Belgium’s division between Dutch- and French-speakers has led to a patchwork of policies on education, social welfare and even security and policing. At the entrance to the national parliament, there are two defibrillators, intended for use in case of heart attacks — one labeled in French and the other in Dutch.

Most of those who left for Syria came from Dutch-speaking Flanders, where a right-wing Flemish nationalist party has been ascendent for years. Critics say the nationalists leave little room for people with different identities. The Flemish part of the country has banned head scarves in many schools.

Compounding the problem, few imams in Belgium speak Dutch — most speak French or Turkish in addition to Arabic. So Muslim youth whose first language is Dutch often turn to the Internet if they have questions about their religious identity.

On the Internet, “it’s not the Islam we have in Western Europe,” Achaibi said, but instead a less inclusive and less tolerant version. But among 165 mosques in Flanders, he said, only 10 imams speak Dutch, a problem that he has been striving to fix.

Analysts say that Muslim youth who feel cut off both from broader Belgian society and their ancestors’ cultures are especially vulnerable to radicalization.

“The Islamic State is giving them what the Belgian government can’t give them — identity, structure,” said Montasser AlDe’emeh of the University of Antwerp, who is researching Belgian fighters in Syria. “They don’t feel Moroccan or Belgian. They don’t feel part of either society.”

And once some people start going to the war, the phenomenon quickly builds on itself.

“If you play football every day in the park and two of your friends go to Syria, you stay in touch with them on Facebook,” AlDe’emeh said. “They say, ‘It’s boring there in Belgium. Here we have nice rivers and Kalashnikovs. Here in Syria we are somebody.’ In Belgium, they’re nobody.”

Initially, analysts say, the Belgian government looked the other way when people started going to Syria. That was at a different stage of the conflict, when it appeared to be an extension of the Arab Spring pro-democracy revolutions. Initially, many Europeans traveled to Syria not out of a desire for jihad but simply because they loathed its longtime leader, President Bashar al-Assad, and wanted to contribute to his ouster.

Then the conflict evolved, with an increasing role played by Islamist militants seeking to build a caliphate — but Europeans kept flowing there. Belgian authorities are worried that some will come back radicalized and launch violent attacks at home. That has prompted them to take far tougher measures to prevent people from heading to the fight.

Fears that yet another Belgian youth was about to leave for Syria motivated investigators to swoop in on the teenager who was detained Friday, said Hans Bonte, the mayor of Vilvoorde, the Dutch-speaking Brussels suburb where the 18-year-old went to school.

“We saw him radicalizing,” Bonte said. “We saw it by following the communications on the Internet, the way he was talking on Facebook, in the classroom.”

“Everything was arranged” for his departure,” Bonte said. “It’s clear that the things happening in Paris and the things happening here accelerated his thinking.”

The detention, he said, “is not the first one, and I fear it won’t be the last one.”