In this Sunday, June 9, 2013 photo, militants who claim that they are ready depart to fight the war in Syria, perform martial art techniques during a show of force in Solo, Central Java, Indonesia. While security agencies in Europe and beyond are worried about militants returning from Syria, Indonesia knows only too well how foreign battlefields, training opportunities and contact with al-Qaida can lead to deadly results. Indonesian anti-terror officials estimated there were around 50 Indonesian militants fighting against the regime of Bashar Assad in Syria and the number is expected to grow. Writings in Arabic on the banner read: "We are the helpers of Allah." In this Sunday, June 9, 2013 photo, militants, who claimed that they are ready depart to fight the war in Syria, perform martial art techniques during a show of force in Solo, Central Java, Indonesia. In this Sunday, Dec. 15, 2013 photo, Muslim men watch a slideshow of pictures believed to be from Syria during a prayer calling for jihad to Syria at a mosque in Jakarta, Indonesia. JAKARTA, Indonesia (AP) - The young Indonesian was raised in an extremist household and graduated from a boarding school notorious for teaching generations of terrorists. So it was perhaps no surprise that when Muhammad Fakhri Ihsani left to study in Pakistan, the lure of jihad proved inescapable. But the 21-year-old didn't sneak into nearby Afghanistan or the lawless border areas, as scores of other foreigners have in recent years. Indonesian authorities believe that after flying to Turkey, he and three other Indonesian students traveled overland to Syria to fight there with fellow countrymen and jihadists from all over the world. Their journey in August shows how determined some Indonesians are to join what has become the new theater of choice for international jihadists. It also points to an emerging threat for Southeast Asian authorities, who have successfully clamped down on militants in recent years, largely preventing them from forging links with their brethren overseas. Indonesian veterans of the Afghan jihad spearheaded attacks in the 2000s against local and Western targets, including nightclub bombings on the resort island of Bali that killed 202 people. The Syrian conflict is also helping fuel an increasingly bitter hate campaign against Shias in Sunni-majority Indonesia, where until a few years ago sectarian divisions, let alone conflict, were largely unheard of. Syrian veterans are only likely to exacerbate this. "We have to learn from our bitter experience in the past," said Ansyaad Mbai, head of the country's anti-terror agency. Every Indonesian who ends up in Syria needs to be watched. We have to anticipate the fact that when they return they will have new abilities and skills in warfare. In interviews, Mbai and two other Indonesian anti-terror officials estimated there were around 50 Indonesian militants fighting against the regime of Bashar Assad, out of up to 11,000 foreigners believed to have become opposition fighters. They said that number is expected to grow. Many were already living or studying in the Middle East when they left. The estimate was based on information from Syrian authorities and their own investigations in Indonesia and Turkey. Indonesian humanitarian groups staffed by hardliners or those with known links to extremists have been raising funds across Indonesia with little transparency. Some are traveling to regions of Syria under the control of militants, treating fighters and handing out cash and relief funds to civilians and local authorities. One organization has traveled at least eight times to the front line in Latakia region, a stronghold of the al-Qaida-linked Nusra Front, according to their literature. Indonesia has more Muslims than any other nation, but the brand and practice of Islam is markedly different from the austere version common in parts of the Middle East and South Asia. Militant Islam has a long history in Indonesia, dating back to the country's birth in 1945, but it has struggled to gain significant followers even as the torch of jihad has been handed down through the generations. The Ngruki boarding school, on the main island of Java, and its network of teachers and ex-students have been central to militant activity in the country since the early 1990s. A close look at those taking part - and advocating for - the war in Syria reveals it remains a central node of extremism, apparently intent on making Syria a new venue for those wishing to take part in jihad. Ihsani and the three other Indonesians who left Pakistan with him attended Ngruki. The first Indonesian known to be killed in the conflict, Riza Fardi, was also a graduate. His death was reported on Arabic jihadi websites in late November, along with a photo of him taken in the region, smiling with other fighters. Bambang Sukirno, another Ngruki graduate and a Bashir associate, took part in a humanitarian mission to Latakia last year, according to video interviews he gave to Islamist media on his return. Sukirno published the autobiography of Bali nightclub bomber Imam Samudra, who writes lovingly of his experience fighting jihad in Afghanistan. "We have learned that some of our alumni are involved in the struggle in Syria, but once again I reiterate that we can't monitor or follow what our students do after they graduate," said Wahyudin, Ngruki's principal. The cleric, who goes by a single name, used a similar defense when confronted with the fact that former students and teachers were convicted of carrying and planning out terrorist attacks inside Indonesia in the 2000s. Ihsani's father, Sholeh Ibrahim, has been a teacher at the school for years, and heads the extremist Jamaah Ansharut Tauhid organization in Solo, where the school is located. JAT is campaigning for Islamic law in Indonesia, is anti-Christian and supports al-Qaida's vision. At least 30 members have been convicted for terrorist offenses over the last four years, and the U.S. State Department declared it a foreign terrorist organization in 2012. The head of the organization nationwide, Abu Bakar Bashir, is serving a 15-year jail sentence for supporting the establishment of a militant training camp. From behind bars, the cleric issued a call for jihad to Syria year. Ibrahim said he last spoke to his son Aug. 21. He didn't mention any travel plans, but asked about his family in Indonesia and spoke of his activities at college in Islamabad, Pakistan, a popular destination for Indonesians looking for cheap degrees in Islam. Ibrahim said neither he nor any of his son's friends have heard from him since. Despite being a proponent of jihad, Ibrahim said he was worried. "Honestly speaking, as father, I'm concerned," said Ibrahim. But I trust in Allah and his will, and I'm sure he (Ihsani) will choose a blessed path. A sustained crackdown by Indonesian authorities since 2002 has reduced the threat of large-scale terrorism against Western or civilian targets in Indonesia and elsewhere in the region. But small groups of militants continue to plot, train for and carry out attacks, mostly against police targets, across the country of 240 million people. Syria represents a rare training and battle opportunity for the current generation of Indonesian militants. Most of the foreign fighters in the country come from the Middle East. Estimates of the numbers of Western European fighters range from 396 to 1,937, according to a recent study by the International Centre for the Study of Radicalization. It's unclear where or with whom the Indonesians are fighting. According to the center, most of the foreigners are grouped with the Nusra Front or the Islamic State in Iraq, the two opposition brigades that are closest to al-Qaida. "Anybody coming back from Syria is going to have immediate credibility and legitimacy in the jihadi movement," said Sidney Jones, the director of the Institute for Policy Analysis of Conflict. There might be people coming back who can take any of these amorphous, feckless groups of extremists and drill them into shape. While the country's extremist fringe is rallying around Syria, it is also apparent most mainstream Indonesian Muslims are not signing up to the cause because it means having to embrace the uncompromising - and still unpopular - sectarian vision that is at the heart of the conflict. Only around 20 people showed up at a recent meeting at a mosque in west Jakarta organized by hardliners who had returned from a Syrian humanitarian mission. A question from a reporter as to why Indonesians should take sides in a civil war in a Muslim country when other causes, for example Palestine, were still pressing, was met with a smattering of applause from those present. Joserizal Jurnalis, a doctor who has led humanitarian missions to help Muslims in Afghanistan, Lebanon and elsewhere, has angered many fellow Indonesian Islamists by refusing to go to Syria or supporting the cause. He says those rallying around Syria are "those close to al-Qaida only." It's a sectarian war. It's not clear to me why we should be helping in the slaughter of other Muslims," he said. Follow Chris Brummitt on Twitter at @cjbrummitt