Four arrested over deadly Jakarta attack

Four men accused of helping to plan the recent deadly attack in Indonesia's capital have been arrested as police continue to crack down on suspected terror supporters.

Officers from the special terrorism task force, Detachment 88, descended on two areas across Indonesia on Tuesday, arresting two men in Cilacap, Central Java and two more in Malang, East Java.

Rifles, revolvers, ammunition and mobile phones were found during the raid in Malang.

"The firearms came from Philippine, Aceh and Syria," national police spokesman Anton Charliyan told reporters on Wednesday.

It is believed all four men have links to the January 14 assault on Indonesia's capital where bombings and shootings killed eight people, including four assailants.

Police allege the men, along with those who carried out the Jakarta attack, were at a December gathering in Malang where they planned the strike.

What their exact role in the assault was, however, is still being investigated.

"We're still investigating how they knew about the plan for the attack," Anton said.

It's alleged the men are supporters of convicted terrorist Aman Abdurrahman who is currently being held in isolation at a prison on Nusakambangan Island in Central Java.

Abdurrahman was recently moved to a high-risk cell after reports four men behind the January 14 attack - Muhammad Ali, Dian Juni Kurniadi, Afif and Ahmad Muhazan - visited him at Kembang Kuning Prison on Nusakambangan Island at least three times since May last year.

Aman was previously translating and disseminating Islamist State messages online and via telephone gatherings from prison.

Anton said arrests like the one Detachment 88 have made this week are the best tools police have to prevent further attacks.

"You might criticise police for being reactive, but if they (terrorist suspects) are not arrested, they would carry out a new attack.

"The effort of prevention is very important. That's why the revision of Terrorism Laws is needed."

While dozens have been arrested since the January attack, only 11 related to the deadly assault remain in custody, Anton said.

The Department of Foreign Affairs and Trade last week warned Australian travellers in Indonesia to exercise a high degree of caution after warnings that terrorists may be well advanced in plans for an attack.