A Batam radio station's line-up of preachers with extreme views appears to have made some long- time followers more receptive to the terror group's radical ideology.
Two such listeners - Singaporeans Rosli Hamzah, 50, and Mohamed Omar Mahadi, 33 - were detained under the Internal Security Act (ISA) this month for planning to travel to Syria to join the Islamic State in Iraq and Syria.
Their cases highlight the danger of exclusivist teachings like those spread by the station, Radio HangFM, in priming individuals for ISIS propaganda, community leaders and experts interviewed said.
While these teachings may not directly encourage violence, they ask believers to stay apart from non-Muslims and Muslims who don't share their views, and this is a slippery slope, they added.
Radio HangFM has been criticised by the mainstream Muslim community in Batam for divisive leanings that, among other things, say Muslims should isolate themselves to maintain their purity.
Ustaz Mohamed Ali, vice-chairman of the Religious Rehabilitation Group (RRG) that counsels terror detainees, said the station may purport to preach Islamic teachings, but listeners must critically assess if what they hear suits the context and environment they live in.
Teachings that exhort believers to keep other communities at arm's length are not suitable especially for Muslims in a multi-religious society like Singapore. "My understanding is that Radio Hang puts out exclusivist preachings," he said. "Such teachings are dangerous, even if they don't preach violence overtly, as they could lead to people being less tolerant and more receptive of violent preachings if there is no intervention."
The latest cases also highlight the danger of learning religion from open sources such as the Internet, social media, TV or radio programmes without having a credible teacher as a guide, said Dr Nazirudin Mohd Nasir, director of religious and policy development at the Islamic Religious Council of Singapore.
"Extremist and exclusivist ideas can be propagated in many ways, over the Internet or the airwaves," he added, stressing that there is no substitute for a proper learning support network of peers, family and especially credible local teachers registered under the Asatizah Recognition Scheme. "It is important that the community continues to be vigilant to the dangers posed by these ideas," he said.
Senior analyst Jasminder Singh of the International Centre for Political Violence and Terrorism Research said it is not too far a stretch that listeners of such stations go on to make contact with like-minded individuals and travel to neighbouring countries, where they may be exposed to more extreme ideology.
In the case of Omar, he came across online material by Al-Qaeda ideologue Anwar al-Awlaki in 2012. He later looked up more radical material, and contacted militants, including a South-east Asian fighter in Syria later killed in combat there.
"Nobody knows if what someone is listening to contains radical ideology, and it is easy to hide such messages inside sermons and talk shows," Mr Singh said.
"It is possible that listening to the radio station made the detainees more receptive to more radical materials later on. It is not yet a trend, but it is something we should be mindful of and guard against."