Thursday's attack in central Jakarta has fuelled the worst fears of south-east Asian governments that Islamic State fighters returning from the Middle East have emerged as a dangerous new threat to the region.

IS has grandiose plans for fighters recruited across the Malay archipelago who have formed a dedicated fighting force called Katibah Nusantara (Malay Archipelago Combat Unit), according to intelligence reports.

Since 2014 the unit has been using videos and printed material in the Malay and Indonesian languages to recruit fighters and supporters in Indonesia, Malaysia, the Philippines and southern Thailand, reports say.

More than 500 Indonesians and dozens of Malaysians are believed to have travelled to the Middle East to fight with IS, mostly in the Katibah Nusantara unit, which last year captured territory held by Kurdish forces in Syria.

The unit's battlefield success has been glamourised in jihadi and IS propaganda disseminated in social media.

A research paper published by the R. Rajaratnam School of International Studies in Singapore last year said that unlike the al-Qaeda affiliate group Jemaah Islamiyah (JI), whose members were mainly returnees from the Afghan war, "this time the region will be confronted with a far stronger force in terms of numbers, ideology and military training and combat experience".

The unit headed mainly by Indonesians has various departments, including those handling combat fighters, snipers, heavy weapons, tactics, strategy and military engagement.

"The growing reach of Katibah Nusantara could lead to its expanding influence in Islamic State's decision-making process, in turn leading to IS giving greater priority to south-east Asia as its war zone," the paper warned.

Analysts say that Katibah Nusantara has connected regional extremist networks, including the remnants of JI, which was responsible for the 2002 Bali bombings that killed 202 people, including 88 Australians.

Singapore's Prime Minister Lee Hsien Loong warned last year that south-east Asia had become a "key recruitment centre" for Islamic State.

"The threat is no longer over there; it is over here," he said.

A series of reports from Malaysia and the Philippines in recent weeks have fuelled fears about the IS threat.

Four radical Islamic groups in the southern Philippines have reportedly pledged allegiance to IS leader Abu Bakr al-Baghdadi and merged to form what could become a potent force.

Seasoned IS fighters are believed to be among them.

Malaysian authorities say they have arrested 150 Malaysians for terrorism-related offences since the formation of IS.

Twenty "seasoned" jihadists were arrested in Malaysia in August last year for planning to bomb bars, discos and the Carlsberg brewer in Malaysia's administrative centre of Putrajaya, officials say.

Twelve others were detained in April carrying 40 kilograms of explosives for attacks on government buildings and police stations.

Malaysia's New Straits Times reported last week that two Malaysian suicide bombers linked to IS had blown themselves up in Syria and Iraq since Christmas, killing more than 30 others.

Malaysia's defence minister Hishammuddin Hussein confirmed the report and warned of the growing role of Malaysians in IS.

Although Malaysian police last week denied the existence of terrorist training camps in the majority-Muslim country. counter-terrorism officials have warned that IS has been indoctrinating and training children to become the next generation of terrorists.

"This threat must be taken seriously," Malaysia's Prime Minister Najib Razak said in a New Year address to the nation.

Analysts also point to links between Katibah Nusantara and Uighur militants from the Chinese province of Xinjiang, who have emerged as another new threat in south-east Asia.

Uighur terrorists are believed responsible to the bomb that killed 22 people and injured more than 100 at the Erawan shrine in central Bangkok in August.

On Christmas Eve Indonesia's anti-terrorism group Detachment 88 raided a safe house in Bekasi West Java and arrested a Uighur militant called Ali, who officials said had been plotting terrorist attacks in Indonesia.

They said "Ali" had joined the network of Bahrun Naim, the Indonesian accused of masterminding Thursday's Jakarta attack.

Officials said Naim had encouraged "Ali" to carry out a suicide mission.

According to intelligence estimates there are more than 1000 Uighur refugees seeking asylum in Muslim communities in south-east Asia.