The unit is called Katibah Nusantara Lid Daulah Islamiyyah, or Malay archipelago unit for the Islamic State in Iraq and Syria.
The Jakarta-based Institute for Policy Analysis of Conflict (Ipac) estimates in a report that the new unit has at least 22 members. They came together in the town of Al-Shadadi, in Syria's Hasaka province, early last month.
Indonesian fighters Bahrum Syah - who appeared in a recent ISIS recruitment video - and Rosikien Nur posted a photo of one meeting on Facebook. The page has since been closed, Ipac said.
Observers say the men appear to have been brought together by language reasons and social media, as many Indonesians found it hard to get along in multinational ISIS units with their limited Arabic and English.
"This group was formed with a goal to recruit and facilitate people who want to go to Syria to defend the Islamic caliphate, and also do counter-attacks against governments that repress caliphate supporters," analyst Robi Sugara of the Barometer Institute told The Straits Times.
Officials say there are more than 50 Indonesian nationals and at least as many Malaysians fighting in Syria.
Reports of the unit came as Malaysia's Foreign Minister Anifah Aman announced to the UN Security Council in New York on Wednesday that his country had designated ISIS as a terrorist group, and vowed tougher action.
Ansyaad Mbai, head of Indonesia's National Counter-Terrorism Agency, said yesterday that he could not comment on the new unit yet.
"But our main concern remains what those who fight there will do when they return," he told The Straits Times.
Asked if they were a threat similar to that posed by Jemaah Islamiah (JI) members from Indonesia, Malaysia and Singapore who returned after training in Afghanistan in the 1990s, he said: "At the core, they share similar beliefs and goals."
Ipac's Sidney Jones said that unlike the JI's South-east Asian Al-Ghuraba cell in the 1990s, which was based in Karachi, Pakistan, and made occasional trips to Afghanistan to train, the ISIS fighters have direct battle experience. "The cross-regional bonds established could also be the strongest we've seen in a long time," Jones added.
Ipac said it was clear from Facebook pages that ISIS supporters in Indonesia and Malaysia were befriending one another. It added that members of the Katibah "could become the vanguard for a fighting force that would reach into Indonesia, Malaysia and the Philippines".
So far, there are no indications of Filipino fighters in the unit yet.
Malaysia's Home Ministry said on Wednesday that it had ordered financial institutions to screen their clients against the UN's terror database and to freeze funds and assets where there is suspicious activity.
The US Treasury has imposed sanctions on JI's humanitarian wing, Hasi, and three Indonesians linked to it - Angga Dimas Pershada, Bambang Sukirno and Wiji Joko Santoso - for raising funds and helping to send extremists to fight in Syria.
The Mindanao-based Abu Sayyaf group and the Bangsamoro Islamic Freedom Fighters have pledged allegiance to ISIS.
Abu Sayyaf this week threatened to execute two German hostages it kidnapped in April, if Germany did not cease its support for US-led strikes on ISIS targets in Syria and Iraq. - The Straits Times/ANN
Did you find this article insightful?