Indonesian police arrested six suspected militants on Friday who they believed to be linked to the Islamic State group and plotting a rocket attack on Singapore, authorities in Indonesia and Singapore said.
Singapore said it was stepping up security in response to the plan to attack it that was being hatched on Indonesia's Batam island, which is only about 15 km (10 miles) to the south of the wealthy city-state.
Members of an elite Singapore police unit patrolled the glittering downtown waterfront in vehicles and on foot on Friday afternoon. One officer said they were on routine patrol.
Indonesian police spokesman Agus Rianto told reporters the six suspects had been plotting with a member of the Islamic State militant group in Syria to attack Singapore, a major commercial, banking and travel hub that is home to many Western expatriates.
"What we understand so far is that they were planning to attack vital objects, busy areas including police offices," Rianto said.
Asked whether police had recovered any physical evidence of a rocket attack, Rianto said "not yet."
Islamic State link
The six arrested were suspected of having links to Bahrun Naim, an Indonesian fighting with Islamic State in Syria, police said.
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.
"There's a link to Bahrun Naim because there was communication with Bahrun Naim - but whether they were affiliated with Bahrun Naim's group or not - this is what we're investigating now," Rianto said.
The Batam Pos newspaper quoted police as saying the six suspects were mostly factory workers aged between 19 and 46.
Batam is linked to Singapore by frequent ferries and its beach resorts and golf courses are a popular weekend getaway destination.
Singapore, which is celebrating its National Day holiday next week, said it is not surprised by the arrests.
"We were aware of the plans being made to attack us with rockets," Home Affairs Minister K. Shanmugam said in a statement.
He did not elaborate on what type of rockets the plotters planned to use or what evidence for the plan had been uncovered.
"The attacks can come from terrorists who seek to come into Singapore; and they can come from terrorists who locate themselves just outside Singapore. Our small size increases these risks," he said.
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 Sept. 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.
Attacks at home
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 neighboring Malaysia say dozens of men have gone from those countries to join IS 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 inIndonesia and other countries to launch attacks at home, instead of being drawn to the fight in the Middle East.
Southeast Asian militants fighting for Islamic State in the Middle East have said they have chosen one of the most wanted men in the Philippines to head a regional faction of the radical group, security officials said last month.
Jakarta-based security analyst Sidney Jones said it would be a departure for Naim and his supporters if they were thinking of attacking targets outside Indonesia.
"One thing I think is clear is Bahrun Naim has been able to establish a lot of communication with a lot of people through his social media network," Jones said.
Singapore's Prime Minister Lee Hsien Loong said this week that the financial center was a target for IS as they saw it as "a rational, open, cosmopolitan country," even though it was not involved in the U.S.-led campaign against the group in the Middle East.
"So do not think that by lying low, we are not going to be a target," Lee told reporters while on a visit to the United States, the Straits Times newspaper reported.
Reporting by Fergus Jensen; Additional reporting by Fathin Ungku and Anshuman Daga inSingapore; Writing by Randy Fabi; Editing by Robert Birsel and Alex Richardson