SYDNEY • The head of Indonesia's national counter-terrorism agency has warned that the Islamic State in Iraq and Syria (ISIS) militant group is working with people-smuggling networks to bring foreign fighters to Indonesia.

In an interview with Australia's ABC News, Mr Saud Usman Nasution said the fighters arrive from Malaysia in Sumatra and are then taken to Poso in central Sulawesi, which is suspected to be a training ground for ISIS fighters.

"First they leave Malaysia and head for Pekanbaru (Sumatra) to Puncak (West Java) - it's all facilitated by asylum-seeker networks - then from Puncak they would leave to Makassar and Poso, with facilitation from the ISIS network," he said.

"So we need to stay vigilant, more so because there is information that in Malaysia, there are thousands, a lot of foreign terrorist fighters there... about to be deployed - we don't know where to - under the ISIS network."

Mr Nasution said it was unclear how many Indonesians have gone to Syria and Iraq to fight with ISIS. However, he disclosed that, so far, 76 Indonesians have returned from the war zones, while 52 died there and four acted as suicide bombers.

"The threat for us is significantly serious," Mr Nasution said.

"There are many radical and terrorist groups in Indonesia that would like to take revenge against what they see as injustice from the West against Muslims. So we need to continue to stay alert, especially after the flock of returnees coming from Iraq and Syria to Indonesia."

Many areas are now under close watch in Indonesia, Mr Nasution said, including the popular holiday destination of Lombok.