Indonesia's counterterrorism chief says his agency is busy working to prevent extremist group Islamic State of Iraq and Syria (ISIS) from spreading its influence across the archipelago.

The National Counterterrorism Agency (BNPT) is tracking activities of ISIS's Indonesian supporters and dissuading young Indonesians from travelling to the Middle East to join the group, BNPT head Ansyaad Mbai told Khabar Southeast Asia.

"We have been monitoring their open support for ISIS, especially through social media," he said.

The BNPT is focusing its efforts on extinguishing the spirit of militant jihad in Indonesia and deradicalising extremists at home, Ansyaad said. "Indonesia had experience with hundreds of individuals waging jihad in Afghanistan back in the late 1990s. ISIS is similar to al-Qaeda.

"All of the jihadists will follow the training as Mujahideen, including the use of weaponry. BNPT's concern is what they will do after returning to Indonesia."

Most Indonesian ISIS volunteers belong to splinter groups Jemaah Islamiyah (JI), Jemaah Ansharut Tauhid (JAT), and the Islamic State of Indonesia (NII), Ansyaad said.

ISIS: the threat to Indonesia

An al-Qaeda-inspired extremist group, ISIS is simultaneously fighting the governments of Syria and Iraq to establish a regional Islamic state. Lately, territorial gains in Iraq by ISIS forces threaten the country's integrity and stability.

Its support base in Indonesia appears to be growing: on June 16th, ISIS supporters rallied in Jakarta.

Indonesian jihadists are believed among the many foreigners in the ISIS ranks. Many young radicals travel from Indonesia to Syria or Iraq via other Middle Eastern countries, noted terrorism expert Taufik Andrie, chairman of the Prasasti Perdamaian Foundation (YPP).

"Our embassies in those countries need to be alert. This is important because of the potentially dangerous impact on Indonesia in the next few years when they return home," he told Khabar.

Also worrisome, Andrie said, are former Indonesian terrorists resuming their terrorist careers in Syria or Iraq.

"Abu Sulaiman Aman Abdurrahman is a former terrorist who was involved in the militant camp in Aceh. In 2010, he was sentenced to eight years in prison. He has reportedly announced his support for ISIS openly on the internet," he added.

Institute for International Peace Building founder Noor Huda Ismail warned the Indonesian government must quickly repatriate citizens engaged in jihad in Syria and Iraq or face the possibility of future dire consequences at home.

"The situation in Syria and in Iraq is more complicated than what we've seen. For Indonesia, the effect can be alarming in the long term," he told Khabar.