Six Indonesians were arrested on Batam island on Friday for planning an attack on Singapore, an Indonesian police spokesman said.

"What we understand so far is that they were planning to attack vital objects, busy areas including police offices," police spokesman Agus Rianto told reporters.

"We also obtained information that these suspects with one ISIS terrorist in Syria now planned to attack Singapore via Batam," he said, referring to the Islamic State militant group.

The six were suspected to have links to Bahrun Naim, an Indonesian fighting for Islamic State in Syria. Naim is believed to be one of the masterminds of an attack in January in central Jakarta, in which eight people were killed including the four attackers.

Batam is just to the south of Singapore.