Indonesians are joining the procession of jihadists to Syria and Iraq, sparking fears they will revive sophisticated militant networks when they return and undermine a decade-long crackdown that has crippled the most dangerous cells.
Support for groups like the Islamic State of Iraq and the Levant (ISIL), Sunni radicals currently rampaging through northern Iraq, is growing among Indonesian extremists with dozens believed to have joined the insurgency.
Analysts say the fighters will pose a new and serious threat to Indonesia when they return home with honed insurgency tactics and international militant connections, echoing the concerns of Western governments.
Britain and Australia have expressed fears that Syria and Iraq are breeding grounds for violent fanatics who travel there from the West to fight and pose a threat to national security on their return.
Indonesia, the world's biggest Muslim-majority nation, has long struggled with terrorism but a successful clampdown in recent years has seen the end of major deadly attacks -- ironically fuelling interest in Syria and Iraq.
"There's not much going on with jihad in Indonesia for militants anymore," said Taufik Andrie, a terrorism expert at the Institute for International Peacebuilding.
"There are just splinter groups with no resources or support, so many are inspired by what's going on in Iraq and Syria," he told AFP.
"When they return, they will be seen as high-profile jihadi. Young people will come to them for training, to form new groups, to plan attacks, to teach how to fight and make bombs."
Indonesia's anti-terror unit has acknowledged that support for ISIL is growing, judging by rallies, social media and the sermons of radical preachers.
The militants have crossed the border from Syria into northern Iraq and taken over key cities in lightning gains, bringing the Iraqi army to its knees.
Indonesia estimates that 60 Indonesians have travelled to Syria and Iraq to fight but experts say the figure is closer to 100 and growing fast.
There are no laws prohibiting Indonesians from joining foreign militant groups and Islamic organisations have openly held fundraisers for ISIL.
"The government must pass legislation to criminalise citizens supporting and travelling overseas to join terrorist groups," Rohan Gunaratna, a terrorism expert at Singapore's S. Rajaratnam School of International Studies, told AFP.
Analysts point to neighbouring Malaysia which has been more active, arresting a dozen men in April who were trying to leave the country to fight in Syria.
