Indonesian authorities said on Monday that several suspected radicals arrested on Batam island last week were part of a group that has "dozens of members" and has been active for two years.
Anti-terror forces arrested six men on Friday on suspicion of planning a rocket attack on neighboring Singapore.
National police spokesman Boy Rafli Amar said the group mostly recruited members online and was taking instructions from Bahrun Naim, an Indonesian who has joined Islamic State in Syria.
"The GRD group has been in operation for two year and has dozens of members," Amar told reporters at a press conference in Jakarta, referring to the group named after its leader Gigih Rahmat Dewa.
Anti-terror personnel rounded up the six men after tracking them for months on social media. One of the suspects was later released, Amar said on Monday.
Police also seized bomb-making materials, guns, and arrows from suspects' homes. But, police said, there were no sign that the rocket attack was anything more than a plan.
"There was no specific timeframe for them to attack Singapore, but that was their target," Amar said.