Indonesian counter-terrorism police arrested six men on Friday suspected of planning a rocket attack on downtown Singapore.
Officers detained the alleged would-be attackers on Indonesia’s Batam Island, about 15 miles from Singapore, the Associated Press reported.
Police said they have yet to find physical evidence of plans to conduct a rocket attack but discovered materials that could be used for explosives, Reuters reported.
“There were no sophisticated arms confiscated, only bomb-making materials,” National Police spokesman Maj. Gen. Boy Rafli Amar told Reuters. He said police are still looking for individuals linked to an Islamic State militant who is based in Syria and suspected of plotting attacks in Southeast Asia.
As Indonesian authorities continued the search for additional militants, Singapore called for increased vigilance, particularly along its borders.
Singapore’s home affairs minister K. Shanmugam, who said the arrested men planned to attack Marina Bay, a popular area featuring entertainment attractions, wrote a cautionary post on Facebook.
“This shows how our enemies are thinking of different ways of attacking us,” the post read. “We have to be extra vigilant.”
Singapore’s Ministry of Home Affairs said in a statement its security agencies coordinated with Indonesia to detain the men.
Police said those arrested, including a 31-year-old suspected of leading the group, claimed allegiance to Katibah Gigih Rahmat, a militant group that helps send Indonesian fighters to Syria.
Authorities said Bahrun Naim, an Indonesian man suspected of fighting with the Islamic State in Syria, directly communicated with the detained men. Naim has participated in planning a number of attacks in his home country, the Associated Press reported, including a suicide bombing in Solo in July.
The bombing last month, in which a militant detonated a bomb at a police station and injured one officer, renewed worries about the presence of terrorism in Indonesia. In January, attacks claimed by the Islamic State killed four civilians in Jakarta, prompting heightened security measures.