Indonesian counter-terrorism police on Friday (August 5) stormed the homes of the suspects believed to be plotting a rocket attack on Singapore.

The raids took place in different locations across Batam, an Indonesian island located just 15 kilometres (10 miles) to the south of Singapore, in the early morning.

Six suspects, believed to be linked to Bahrun Naim, an Indonesian fighting with Islamic State in Syria, were arrested on Friday as Singapore stepped up its security in response to the planned attack.

Indonesian investigators believe that Naim was one of the masterminds behind an attack in January in the Indonesian capital of Jakarta, in which eight people were killed including the four attackers.

Indonesian authorities did not confirm details of the latest alleged plot.

National police spokesman Martinus Sitompul said police and an anti-terrorist unit were in the early stages of their investigation.

Authorities in Indonesia and neighbouring Malaysia say dozens of men have gone to join Islamic State in the Middle East, while Singapore has detained several people suspected of supporting the group.

Security officials fear that Naim and other Islamic State leaders were now asking supporters in Indonesia and other countries to launch attacks at home, instead of being drawn to the fight in the Middle East.

Multi-ethnic Singapore has never seen a successful attack by Islamist militants, though authorities did break up a plot to bomb several embassies soon after the September 11, 2001, attacks on the United States, while jailed Singaporean militant Mas Selamat Kastari was accused of plotting to crash a hijacked plane into the city-state's Changi Airport in 2002.