JAKARTA - Several hundred supporters of hardline groups gathered at a mosque in Solo, central Java, on Tuesday to show their support for Abu Bakr al-Baghdadi, leader of the recently declared caliphate of the Islamic State in Iraq and Syria (ISIS).
A similar gathering is planned on Sunday in Malang, East Java.
These come on top of two similar ISIS gatherings that had already been held near Jakarta and in Bima this month, raising concerns about young Indonesians travelling to the battlefront and returning to carry out terror attacks back home.
A group of Indonesian radicals has already claimed the status of ISIS' Indonesian chapter, and at least one ISIS flag was spotted last Friday at a Jakarta demonstration against Israeli attacks on Gaza.
Counter-terrorism officials say they are keeping close tabs on these groups.
"We are on the alert," Mr Harry Purwanto, deputy for international cooperation at the National Counter-Terrorism Agency (BNPT), told The Straits Times, noting that many of these events are also widely publicised on social media and radical sites.
"But we also have to empower civil society to have the courage and confidence to challenge these radical groups," he said.
The hardline groups are exploiting a loophole in Indonesian law, which does not criminalise incitement to terror or support for terrorist groups. This means the authorities need a higher threshold of evidence to apprehend militants, often when their plans are under way.
BNPT estimates that some 50 militants have travelled to Syria and Iraq, and are concerned that they could engage in terror on their return, just as an earlier generation of Jemaah Islamiah members did after fighting in Afghanistan in the 1990s.
There are other concerns. This week, radical websites reported jailed cleric and Jemaah Ansharut Tauhid (JAT) founder Abu Bakar Bashir expressing support for ISIS, though he stopped short of swearing loyalty to al-Baghdadi.
BNPT chief Ansyaad Mbai told The Jakarta Post that Bashir had also been actively seeking donations and recruiting fighters for ISIS.
Analysts note that while Bashir has held back from swearing allegiance to al-Baghdadi, he has had to tread carefully to avoid alienating his supporters, as more hardline militants openly swear to help ISIS. Bashir is serving a 15-year sentence for terrorism.
Earlier this month, the Eastern Indonesia Mujahideen (MIT), led by Sulawesi-based terrorist Santoso, uploaded an audio message to YouTube pledging allegiance to al-Baghdadi.
Mr Robi Sugara of the Barometer Institute told The Straits Times that JAT's lack of support for ISIS has seen some members leave the group.
"There is still strong tension within JAT between those who are pro-ISIS and those who are not," Mr Robi said.
ISIS, meanwhile, has found support among other Indonesian radical groups such as the Forum of Activists for Islamic Syariah (Faksi) and Islam Reform Movement (Garis).
Mr Harry of the counter-terrorism agency said that these supporters have a similar mindset to hardliners. Thus the possibility that they may resort to attacks at home cannot be ruled out.
"Like all terrorists, they seek maximum publicity through maximum damage," he said.
This article was first published on July 17, 2014.
Get a copy of The Straits Times or go to straitstimes.com for more stories.