An audacious attack by suicide bombers in the heart of Indonesia’s capital was funded by the Islamic State, police said Friday as they said they seized one of the group’s flags from the home of one of the attackers and carried out raids across the country, in which one suspected militant was killed.

Gen. Badrodin Haiti, the national police chief, told reporters that Islamic State funding for Thursday’s attack was funneled through an Indonesian, Bahrun Naim, who spent one year in prison for illegal possession of weapons in 2011 and is now in Syria fighting for the group.

Supporters of the militant group also circulated a claim of responsibility for the attack on Twitter late Thursday. The group controls territory in Syria and Iraq, and its ambition to create an Islamic caliphate has attracted some 30,000 foreign fighters from around the world.

The Islamic State link, if proved, poses a challenge to Indonesian security forces. Until now, the group was known only to have sympathizers with no active cells capable of planning and carrying out a plot such as Thursday’s, in which five men attacked a Starbucks cafe and a traffic police booth with handmade bombs, guns and suicide belts. They killed two people — a Canadian and an Indonesian — and wounded 20 in the first major attack in Indonesia since 2009. The militants were killed, either by their suicide vests or by police.

The attack “was funded by ISIS in Syria through Bahrun Naim,” Haiti told reporters after Friday prayers, using an acronym for the group. He did not elaborate.

1 of 15 Full Screen Autoplay Close Skip Ad × The scene after suspected Islamic State affiliates stormed Indonesia’s capital View Photos Militants staged suicide bombings and opened fire in downtown Jakarta. Caption Militants staged suicide bombings and opened fire in downtown Jakarta. Jan. 14, 2016 People, including unarmed police officers, flee from the scene after a gun battle broke out following an explosion in Jakarta. Attackers set off bombs and exchanged gunfire outside a Starbucks cafe in Indonesia's capital in a brazen assault. AP Buy Photo Wait 1 second to continue.

He also identified one of the five attackers as Afif Sunakim, who in 2010 was sentenced to seven years in jail for his involvement in military-style training in Aceh, but was released early.

Police conducted raids across Indonesia, but was it unclear whether those arrested were suspected of links to the bombing or if police were rounding up militants as part of a broader crackdown in its aftermath. They also outlined a partial reconstruction of events based on security camera video, part of which showed a Starbucks customer escaping from the grip of an attacker before he detonated his suicide bomb.

Maj. Gen. Anton Charliyan, a national police spokesman, said raids were conducted in Java, Kalimantan and Sulawesi, with four arrests made. Charliyan said three men arrested in Depok on the outskirts of Jakarta are no longer suspected of being linked to the attack. On Friday evening, police searched the home of another of the dead bombers, whom they identified as Muhammad Ali (no relation to the former professional boxer).

Amateur video obtained by Reuters shows militants shooting at civilians and security forces during Thursday's attack in Jakarta, Indonesia. (Reuters)

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