Militants from Indonesia and Malaysia fighting in Syria have come together on common language and culture, forming their own military unit and prompting fears of the Islamic State in Iraq and Syria's (Isis) expansion in Southeast Asia, a Jakarta think tank warned.

Quoted by Singapore's The Straits Times (ST), the Institute for Policy Analysis of Conflict (Ipac) said 22 members had formed the "Katibah Nusantara Lid Daulah Islamiyyah" (Malay archipelago unit for the Islamic State) in Al-Shadadi, Syria, as appeared in a video posted on a Facebook page which has since closed.

The daily said faced with language barriers, the new unit would make it easier to recruit Indonesians who could not communicate in English or Arabic.

"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," the paper quoted Robi Sugara of the Barometer Institute as saying.

ST also quoted Ipac's Sidney Jones as saying that unlike Jemaah Islamiyah, al-Qaeda's regional chapter blamed for a spate of terrorist attacks in Indonesia, Isis fighters already had battle experience.

"The cross-regional bonds established could also be the strongest we've seen in a long time," Jones told the daily.

She said a check on Facebook revealed that pro-Isis Indonesian and Malaysians were linking up, and warned that the newly formed Katibah "could become the vanguard for a fighting force that would reach into Indonesia, Malaysia and the Philippines".

The revelation of the new group comes as Malaysian police reportedly detained three men who were allegedly on the way to Istanbul via Doha to join Isis forces.

Officials in Indonesia and Malaysia have detected scores of their citizens fighting for Isis in Syria.

22 Malaysians have so far been arrested for links to Isis, and police are now tracking down five militants believed to be connected to Isis and Abu Sayyaf, the Philippines-based terror group.

On September 24, Defence Forces chief General Tan Sri Zulkifeli Mohd Zin warned that Isis was a real threat, adding that the authorities should take action to prevent it from turning into a major problem.

Referring to the Malaysians involved in militant activities in Syria and Iraq, he told Bernama he was “worried that when they return to Malaysia, they will do something that can threaten the safety of the country, especially after they established a network in neighbouring countries from Syria or Iraq”.

Meanwhile, a senior Malaysian intelligence official told The Malaysian Insider on September 22 that Isis forces were using social media platforms such as Facebook to enlist fighters from around the world, adding that some 40 Malaysians had been thus recruited.

“Terrorist groups are adapting their tactics and evolving out of necessity because of far-reaching, multinational counter-terrorism operations abroad,” the official said.

“The strategy of bringing like-minded people together via conversational media increases the radicalism of jihadists.”

On September 14, former PAS member Lotfi Ariffin died in Syria after succumbing to injuries suffered while fighting alongside Isis forces.

Lotfi had reportedly been with a group of Malaysian Isis fighters when they were caught in an ambush by forces loyal to Syrian President Bashar Al-Assad.

Last month, The Malaysian Insider reported that Malaysian women are believed to have joined Isis forces to offer what is called “Jihad al-Nikah” or “conjugal jihad”.

Senior intelligence officials later confirmed that three Malaysian women had journeyed to the Middle East to join up with Isis forces. – September 26, 2014.