An Indonesian anti-terror policeman (Gegana Brimob) stands guard next to the Starbucks cafe after several blasts and shootings in Jakarta on Jan. 14, 2016. ADEK BERRY/AFP/Getty Images

UPDATE: 6:45 a.m. EST — Indonesian police named one of the attackers behind Thursday’s assault in Jakarta that left seven people dead, including five suicide bombers and gunmen. The attacker, Afif Sunakim, was a militant who was given a seven-year jail term for attending a militant camp, BBC reported.

Authorities reportedly said that they have established the identities of four of the five attackers. Gen Badrodin Haiti, the national police chief, reportedly said Sunakim and one other attacker were both convicted criminals.

Police also said Friday that they killed one suspected militant and arrested two others during raids across the country. The militant was killed in a gun battle in Central Sulawesi, while two others were arrested in the city of Cirebon in West Java, Reuters reported, citing police. While the three men were reportedly suspected to be ISIS supporters, they were not directly linked to Thursday’s attack in Jakarta, police said.

"It's clear that the (Jakarta attackers) didn't set this up themselves. For this, we are searching for the networks and who was involved in this action," Anton Charliyan, national police spokesman, reportedly said.

Original story:

An Islamic State group flag was found with one of the attackers behind Thursday’s assault in Indonesia’s capital city of Jakarta and police said they have established identities of the attackers involved, national police spokesman Anton Charliyan said Friday, according to the Associated Press (AP). Seven people, including five suicide bombers and gunmen, were killed during the attacks at a Starbucks cafe and a traffic police booth.

Charliyan reportedly said that two of the five men involved in the attacks were previously convicted and imprisoned for terrorism offenses. However, he did not reveal the identities. The black ISIS flag was reportedly found at the home of one of the attackers and the discovery supports claims that the attack was carried out by ISIS, which controls territory in Iraq and Syria and aims to establish an Islamic caliphate around the world.

Details emerged about the attackers just as police told an Indonesian TV channel that three men have been arrested on suspicion of having links to the attacks, which has sparked concerns over the rise of ISIS in the Southeast Asian nation.

The three arrests were made during raids on homes in Depok on the outskirts of Jakarta, AP reported, citing police. The raids were reportedly headed by Col. Khrisna Murti, director of criminal investigations.

The first attack by the radical group in Indonesia, the world’s most populous Muslim nation, poses a grave challenge to the country’s security forces.

"We need to pay very serious attention to the rise of ISIS," Jakarta police chief Tito Karnavian said Thursday, according to Reuters. "We need to strengthen our response and preventive measures, including legislation to prevent them ... and we hope our counterparts in other countries can work together because it is not home-grown terrorism, it is part of the ISIS network."

ISIS said, while claiming responsibility for the attacks, that "a group of soldiers of the caliphate in Indonesia targeted a gathering from the crusader alliance that fights the Islamic State in Jakarta.” The message was circulated by ISIS supporters on Twitter late Thursday. The U.S.-based SITE Intelligence Group reportedly said that the message was also circulated among pro-ISIS groups on the message app Telegram.