JAKARTA -Indonesia's Riau Islands province, which consists of huge tracts of open seas, is vulnerable to infiltration by terrorists and must be closely monitored, said the head of the country's National Counterterrorism Agency's (BNPT) Suhardi Alius.

He said that 96 per cent of the province, referred to by its Indonesian acronym Kepri, consists of open seas, and it the gateway from Malaysia and Singapore.

Kepri includes Batam and Bintan islands along with the Anambas and Natuna islands far to the north-east of Singapore.

Commissioner General Suhardi, speaking to hundreds of security personnel on Batam island on Thursday (Feb 22), referred to several cases of radical groups using Kepri as their base, according to Kompas news site.

He said the province was also used as a transit point by Indonesians heading to Syria and by militants heading to Indonesia's Poso island, which was wracked by religious conflict.

A group of Indonesia terrorists are now in jail for planning to fire a rocket at Singapore's Marina Bay from Batam in August 2016.

Kepri's police head Inspector-General Sambudi Gusdian said in June last year thatthe province has strengthened security measures and monitoring activities in ports of entry and outermost islands to prevent terrorists from infiltrating it.

The extra measures were taken following terror attacks in several countries and in response to the situation in Marawi, southern Philippines, which were occupied by terrorist last year.