Singapore has deported eight Indonesians, after immigration officers at Woodlands Checkpoint found a photo of a "shoe bomb" in the smartphone of the group's leader.
The men, from Bukit Tinggi in West Sumatra, had travelled to Thailand and Malaysia over the past week. They were handed over to the Malaysian authorities, and subsequently sent to the Riau Islands on Tuesday.
Riau Islands police chief Sam Budigusdian said on Wednesday that the group is now being questioned by officers from Detachment 88 (Densus 88), Indonesia's police counter-terrorism unit.
Singapore's Ministry of Home Affairs yesterday confirmed that the men, aged between 16 and 37, were deported to Malaysia, as one of them was in possession of "images of security concern", including that of a shoe bomb and another of fighters from the Islamic State in Iraq and Syria (ISIS).
General Sam said the men were from a boarding school for Muslims in Bukit Tinggi and members of Jamaah Tabligh, an Islamic missionary movement.
They left Padang in West Sumatra on Jan 3 and flew to Kuala Lumpur to preach in Bukit Jalil.
The 37-year-old group leader, identified by the initials REH, was also there to seek treatment for an ear infection, he added.
Over the next two days, they travelled overland to mosques in Malacca and Perlis, before making their way to Pattani, a town in southern Thailand on Jan 7.
"Then on Jan 10, they tried to enter Singapore, but they were denied entry and later handed over to Malaysia," said Gen Sam.
Malaysian state news agency Bernama reported yesterday that the group was stopped by the Singapore authorities at 1.30am on Tuesday.
The Straits Times understands that investigators are still trying to establish what the group was doing between Jan 7 and the day they arrived at Woodlands Checkpoint.
According to Gen Sam, Malaysian investigators had concluded that the group of eight did not embrace ISIS ideology and REH had downloaded the illicit images into his smartphone from a WhatsApp group, which he has since left.
"Densus 88 has a week to conduct its investigation against them. We are still trying to determine (what happened)," he added.
Indonesia's anti-terror laws do not allow the police to detain a terrorist suspect for more than seven days for questioning.
This is the third report in the last year of Indonesians being deported by Singapore over suspected links to ISIS.
Last month, two Indonesians - a woman and a man - were deported to Batam after it was established that the woman, Suriati, had planned to join ISIS. She was detained after she arrived at HarbourFront Centre on Dec 26.
That same day, the man, M. Nur, landed at Changi Airport and was questioned. Both were deported after it was established that Suriati had intended to travel to Syria with help from M. Nur.
This came after four Indonesians from an Islamic boarding school in West Java were stopped in Singapore and deported last February after they were found to have plans to travel to Syria to fight for ISIS.
Security analysts foresee more of such cases as the group expands its influence in Indonesia.
Associate research fellow V. Arianti of the International Centre for Political Violence and Terrorism Research said: "The recruitment of new members... in the country indicates ISIS' continued appeal."