A prominent expert on Islam is criticising the Islamic State in Iraq and Syria's (ISIS) extremist ideology as being unrealistic for Indonesia and out of touch with popular sentiment.

ISIS's recent declaration to establish a caliphate led by Abu Bakr al-Baghdadi encompassing parts of Syria and Iraq lacks legitimacy, according to Jakarta State University rector Komaruddin Hidayat.

"The concept of a caliphate is now part of the history in Islam. It has already been replaced with the nation-state and democracy. That means [power] is not centralised under one person's leadership," Komaruddin told Khabar Southeast Asia.

He believes Indonesians would never accept a caliphate.

"Indonesia has many moderate Muslims, and they are not interested in this concept," he added.

Jemaah Islamiyah (JI) founder Abu Bakar Bashir 's reportedly endorsed ISIS's caliphate.

Many Indonesian extremists have answered Bashir's call to support the caliphate, but mainly out of anger over the situation in the Middle East, Komaruddin said.

"This is not what we have in Indonesia," he added.

Bashir's involvement

Mochammad Achwan, leader of the hard-line Indonesian group Jamaah Ansharut Tauhid (JAT) , told The Jakarta Post that the imprisoned JI leader had notified JAT of his support for jihadists fighting for ISIS.

"It is because ISIS will rule according to sharia, has a clear leadership, and is already established," Achwan told reporters. He also acknowledged that several JAT and JI members travelled to the Middle East to join ISIS and Jabhat al-Nusra (JN).

The Indonesian government is responding by cracking down on Bashir's supporters who are trying to leave the country, National Counterterrorism Agency (BNPT) chief Ansyaad Mbai said.

"Bashir's followers had collected some funds and recruited volunteers. Internally, we have already arrested many of his members," Ansyaad told Khabar. "From our investigation, we know how Bashir is involved.

"We will continue to monitor any extremist organisations that exist in Indonesia, including JI, JAT, Majelis Mujahidin Indonesia (MMI) and the Indonesian Islamic State (NII) . They have similar ambitions."

A new generation of Mujahideen

Authorities also are keeping a close eye on movements of Indonesians taking part in humanitarian missions in the Gaza Strip and trying to weed out those seeking to join jihadist efforts in Syria and Iraq, said Harry Purwanto, the BNPT's deputy for international co-operation.

"It is a complex situation," Purwanto told Khabar. "At this point, we hope that they will return home after they finish with their mission helping the victims in Gaza.

"We have learned from the prior case of Afghan combatants back in 1999, and we should anticipate this happening."