Indonesian police on Friday arrested six suspected Islamist militants, one of whom had allegedly considered launching a rocket at Singapore's Marina Bay, a spokesman said.
The six were arrested in three separate locations on Batam island, just south of Singapore, national police spokesman Boy Rafli Amar said.
The suspects are linked to Bachrun Naim, a wanted Indonesian militant thought to be fighting alongside the Islamic State group in Syria, Amar said.
Among those arrested was Gigih Rahmat Dewa, who according to Amar had plotted together with Naim to launch a rocket from Batam at Singapore's Marina Bay.
"[Dewa] also helped facilitate trips by Indonesians to Syria via Turkey," Amar said.
Singaporean security agencies had coordinated with their Indonesian counterparts in the run up to the arrest, the Singaporean government said, adding that local security would be stepped up.
"This does not come as a surprise," Singaporean Home Affairs and Law Minister K Shanmugam said in a statement cited by local media. "I have spoken several times about plans being made in places just outside Singapore, to target Singapore – we were serious about the threats."
Indonesia, the world's largest Muslim-majority country, has suffered several deadly attacks blamed on Islamist militants since the early 2000s.