A number of jihadist groups in Southeast Asia have pledged loyalty to the Islamic State (ISIS/ISIL), and up to 1,000 people have left Malaysia, Indonesia, and the Philippines to join the terrorist organization in Iraq and Syria, reports BBC.

Abductions by the ISIS-linked Filipino group Abu Sayyaf have recently prompted Indonesia to call for joint maritime patrols with the Philippines and Malaysia.

“Several countries in Southeast Asia have been anticipating attacks by the so-called Islamic State (IS) group in the region,” notes BBC.

“Indonesia, Malaysia and Singapore warned their citizens in 2015 that it was a question of when, rather than if, they would take place and this foresight was sadly proven right with the attack on Jakarta in January this year,” it adds.

Citizens of Indonesia and Malaysia have reportedly formed an official ISIS branch known as Katibah Nusantara Daulah Islamiyah.

“Security experts believe its leaders are trying to fund and encourage attacks across the region,” notes BBC, referring to the wing of the Islamic State, also known as IS. “Over the past year, IS has increased its propaganda efforts in Indonesian, which is similar to Malay, inciting people to join it but also to carry out attacks where they are.”

Authorities in Southeast Asia have reportedly been on alert for foreign jihadists who may travel to the region to share or pick up battlefield knowledge.

“Militant groups in the region are known to work together and fighters sometimes travel to another country to evade arrest in their own,” points out BBC. “South East Asia’s long coastlines and porous borders make it difficult for the authorities to monitor or stop such movement.”

The report adds:

In the last few months, the Philippine army has killed two Malaysians fighting with Abu Sayyaf in the south. Indonesian authorities have arrested four Uighurs from China over links to the Mujahidin Indonesia Timur (MIT) group in Sulawesi, and recently killed two who were fighting with MIT. Militants from Syria, Iraq and Turkey have also been sighted in the region, and arrested in some cases over planned attacks.

The Philippine-based Abu Sayyaf group, which has pledged allegiance to ISIS, recently beheaded one of its foreign hostages after the captive’s government failed to pay a ransom worth millions of dollars.

“Security experts believe competition to lead a potential official IS regional province may spur further attacks,” reports BBC. “IS has acknowledged pledges by some groups in the region but not yet formally declared it a ‘province’ as it has with other areas, such as Boko Haram in Africa, though there are signs it is moving toward doing so.”