Jakarta. Counterterrorism squad Detachment 88 has arrested 13 suspected members of shadowy militant network Jemaah Islamiyah, or JI, during separate operations across Sumatra, the National Police said on Friday.

While most recent attacks have been largely attributable to home-grown group Jemaah Ansharut Daulah, security officials repeatedly warned that JI cells remain active and are recruiting members.

The JI is blamed for major attacks in the 2000s, including the October 2002 Bali bombings that killed more than 200 people of mostly foreign holidaymakers, the bombing at the Australian Embassy in Jakarta in 2004, and the twin hotel bombings in Jakarta in 2009.

During the raids on Thursday, four suspects were arrested on Batam Island off Sumatra's eastern coasts and nine others were captured in the North Sumatra districts of Medan, Langkat, Binjai, and Tanjung Balai, according to Chief Comr. Aswin Siregar, the elite unit’s operational support division head.

When contacted, the National Police declined to disclose the identities of the suspects and their charges pending further investigation.

“They are believed to be JI members,” National Police spokesman Brig. Gen. Rusdi Hartono said briefly.

Police said earlier the JI has been actively raising funds by deploying charity boxes at minimarkets in several regions throughout Indonesia to trick the unsuspecting shoppers into giving money that would fund the group's activities. 

The money was used to send militants to war zones like Syria and acquire weapons and explosives, among other things.

Hundreds of donations boxes were seized during recent operations in the province of Lampung.