JAKARTA (REUTERS) - Indonesia's counter-terrorism police plan to arrest more than 100 suspected militants in a bid to prevent retaliatory attacks after a radical cleric linked to the Islamic State in Iraq and Syria (ISIS) was sentenced to death, the country's police chief said on Thursday (June 28).

Aman Abdurrahman, regarded as the ideological leader of Jemaah Ansharut Daulah, a loose grouping of hundreds of ISIS sympathisers, was convicted last month for masterminding four deadly attacks in Jakarta and elsewhere in Indonesia.

He has been in prison since 2009, but was accused of orchestrating the attacks from behind bars. No date has been set for Abdurrahman's execution, which is likely to be by firing squad, but in the meantime Indonesian security forces have been put on high alert.

"The price we have to pay is the possibility of his networks retaliating," General Tito Karnavian told Reuters in an interview at the national police headquarters.

"But the good news is we have detected most of his networks and cells...More than 100 of them will be arrested. We have to move before they move," said Gen Karnavian, who previously headed Indonesia's elite counter-terrorism squad Detachment 88, known locally as Densus 88.

The Southeast Asian nation has faced a surge in homegrown militancy in recent years and around 30 people were killed in suicide bombings in Surabaya last month, marking the deadliest militant attack in over a decade in the Muslim-majority country.

The attacks on three churches and a police station in Surabaya were carried out by families, who took children as young as eight on their mission, marking the first time such a tactic had been used, according to terrorism experts.

Gen Karnavian said authorities had been aware of the risk of female suicide bombers, but had no information that a whole family unit or children would be used to carry out bombings.

The families behind the attacks had been monitored by authorities for four months last year, but there had been no suspicious activity involving the children, he said.

Since the Surabaya attacks, the police have detained more than 120 suspects and killed 17.

One key suspect, Kholid Abu Bakar, who officials believe was the leader of the attackers' Islamic study group, remains at large.

Gen Karnavian said Bakar and his family had attempted to travel to Syria last year to join ISIS but were caught in Turkey and deported back to Indonesia.

Gen Karnavian said surveillance teams in Indonesia had now been doubled and provincial police headquarters instructed to set up joint teams involving local-level military, intelligence, and paramilitary police. In the wake of the attacks, Indonesia toughened up its anti-terrorism laws last month to allow police to arrest and detain suspected militants for longer periods, and without having to wait until they acquired weapons or carried out attacks.

"It gives us more room to manoeuvre. It is much, much easier because we don't need to watch and wait until they possess weapons," he said.

But expanded authority or firepower may not always be enough to foil attacks, Gen Karnavian said, calling for deradicalisation programs to be strengthened.

"I believe Densus 88 is good enough in monitoring people, foiling plans and investigating attacks....But there is no use in this hard approach if we cannot change their mindset."