Aman Abdurrahman and his cellmate Iwan Darmawan Muntho, alias Rois, will face charges for their roles in the planning of the Jan 14 attacks in Jakarta, the capital's police chief Tito Karnavian said.

He added that the process to prosecute both men, now in Nusakambangan maximum-security prison for separate terror-related activities, has started after police found links to the four militants who mounted the January strike.

Inspector-General Tito, who was responding to a question from The Straits Times during a university seminar on Thursday, said Aman is scheduled to be released in 2018.

However, investigators are building a case against the radical ideologue as a suspect "because he is the mastermind" of the recent attack, Inspector -General Tito added.

Rois, who is on death row for his part in the 2004 bombing of the Australian embassy in Jakarta, may also see his execution date brought forward in view of the fresh charges.

Said Inspector-General Tito: "He is on death row, so for him he has nothing to lose. But we will still prosecute him in relation to the Thamrin attack and, if he is convicted, this may serve as a strong reason to accelerate his execution."

Evidence against Aman and Rois has been mounting in recent weeks, following the arrest of nearly 40 suspects in connection with the attack along Jalan M.H. Thamrin.

Indonesia's national police chief, General Badrodin Haiti, said yesterday that at least 16 of those detained were found to have been directly involved, and police are tracking one more person still at large.

Aman apparently conveyed the order from the Islamic State in Iraq and Syria to hit Jakarta, while Rois helped them with military tactics.

Francis Chan and Wahyudi Soeriaatmadja