Singapore said on Friday it had stepped up its border and inland security after Indonesian police arrested six suspected militants on the nearby Indonesian island of Batam suspected of planning an attack on Singapore.

"MHA (Ministry of Home Affairs) is aware that plans were being made by the six terror suspects arrested by the Indonesian Authorities," the ministry said in a statement on Friday.

"Our security agencies have been coordinating closely with the Indonesian authorities since the discovery of this attack plot, to monitor the activities of the group and to apprehend those involved."

The ministry said police and other agencies had been stepping up inland and border security measures in response to the threat.

Multi-ethnic Singapore has an image as one of the safest countries in the world and has never seen an attack by Islamist militants.