Indonesia's elite anti-terrorism squad launched an investigation into the twin suicide-bomb attack in Jakarta that killed three policemen in an assault authorities believe was linked to ISIL.

Authorities on the island of Java on Thursday raided the homes of two men suspected of blowing themselves up in Wednesday night's attack on a bus terminal in the capital.

Three police officers were killed, while six others and five civilians were wounded in an assault that left body parts and shattered glass strewn across the street.

"Terrorism is a serious reality that we are facing right now and it's a global problem. What is happening in other parts of the world can become an inspiration for other sleeper-cells somewhere else," said Indonesia police spokesman Setyo Wasisto on Thursday.

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Police said they believed there was a link between the attackers and Islamic State of Iraq and the Levant (ISIL, also known as ISIS), without giving further details.

Hundreds of Indonesians have flocked abroad to fight with the armed group in Syria and Iraq, and ISIL-linked combatants have been accused of being behind a series of recent plots and attacks across Indonesia.

The bus station bombing was the deadliest to hit in Indonesia since January 2016, when a suicide blast and gun assault claimed by ISIL in downtown Jakarta killed four civilians, along with four attackers.

In a televised address, President Joko Widodo said he ordered a thorough probe and was "urging all citizens across the nation to stay calm and remain united".

Police said they believe officers were specifically targeted in the bombing.

"Since 2010, the police have been a major target partly because there's a sense of wanting revenge against the police since they're the ones that go after the terrorists," Sidney Jones from the Institute for Policy Analysis of Conflict told Al Jazeera.

The attack came as police prepared to provide security for a traditional parade ahead of the fasting month of Ramadan near the Kampung Melayu terminal, an area frequented by locals but not foreigners.

The elite police squad Densus 88, which has played a leading role in tracking down and killing some of Indonesia's most wanted fighters, is now taking the lead in the investigation.

Pressure-cooker explosive

In a raid on Thursday morning of one bomb suspects' house in Bandung city, police discovered religious literature and two bladed weapons, West Java province police spokesman Yusri Yunus told AFP news agency.

Relatives of both men, whose identities have not been released, were taken in for questioning, he said.

Asked whether there were ties between ISIL and the attack, national police spokesman Awi Setyono responded "yes there is", without providing further information.

Suspicion is likely to fall on local network Jamaah Ansharut Daulah (JAD), which supports ISIL and has been blamed for recent mostly low-impact attacks.

The bombs used in Wednesday's attacks were made from pressure cookers, similar to a device used in an attack by a JAD member in the Indonesian city of Bandung in February.

Another figure who may come under scrutiny is Indonesian man Bahrun Naim, who is fighting with ISIL in Syria and has been accused of directing a series of mostly botched plots in his homeland.

Indonesia has long struggled with hardline armed groups and has suffered a series of attacks in the past 15 years, including the 2002 Bali bombings that killed 202 people, mostly foreign tourists.