Singapore called for heightened vigilance on Saturday, a day after Indonesian police arrested a group of men they believed were plotting a rocket attack on the wealthy city-state with the help of a Syrian-based Islamic State militant.
The six suspected militants were rounded up on Friday in dawn raids on Batam island, about 15 km (10 miles) south of Singapore, where police believe the men planned to fire the rockets from.
Local police chief Sam Budigusdian said those arrested were still being held there while investigations continued.
Singapore's home affairs minister, K. Shanmugam, said the men had plans to hit Marina Bay, the state's glittering downtown waterfront, where night-time Formula One Grand Prix Races are held alongside a giant ferris wheel and a swanky casino resort.
"This shows how our enemies are thinking of different ways of attacking us," Shanmugam said in a Facebook posting.
"Terrorists ... will seek to come in through our checkpoints; they will also try to launch attacks from just outside. And this is in addition to lone wolf attacks from radicalised individuals/groups. We have to be extra vigilant."
Batam is linked to Singapore by frequent ferries and its beach resorts and golf courses are a popular weekend getaway destination for Singaporeans, who are preparing to celebrate their National Day holiday on Tuesday.