MANILA - At least two terrorists from Sri Lanka have sneaked into the Philippines to train local militants on making bombs and attacking churches and other soft targets north of the country.

A watch list from the Manila International Airport Authority identified the two as Mark Kevin Samhoon and Victoria Sophia Sto Domingo. Both were tagged as "suicide bombers", with kin in the Philippines.

Samhoon has ties to the National Thowheed Jamath (NTJ), the terrorist group accused of carrying out the Easter Sunday attacks in Sri Lanka in April this year that killed at least 250 people, according to the watch list. His mother is a Filipino working as a maid in Dubai.

Samhoon is said to be "connected" to Sto Domingo, though it is unclear what is the link between them.

Sto. Domingo is described as a "black-belter" who had trained children and women in bomb-making. She holds a Philippine and a Sri Lanka passport.

She arrived in the Philippines in November 2018. Samhoon followed her, possibly in June this year.

Mr Rommel Banlaoi, head of the Philippine Institute for Peace, Violence and Terrorism Research, told The Straits Times that Sto Domingo was involved in plotting the suicide attack in January this year on a Roman Catholic cathedral in Sulu province, that killed 23 people and wounded at least 100. Indonesian police tagged Indonesians Rullie Rian Zeke and Ulfah Handayani as the bombers.

BenarNews reported that Samhoon and Sto Domingo were already with a faction of Filipino militants in the main Philippine island of Luzon, some 1,000km north of where most extremist groups linked to the Islamic State in Iraq and Syria (ISIS) normally operate.

A group called Suyuful Khilafa Fi Luzon, formed by remnants of the Rajah Sulaiman Islamic Movement, is purportedly planning to bomb churches in Luzon, with help from Samhoon and Sto Domingo.

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The capital Manila and other densely populated cities are in Luzon.

Militants are seeking to bomb targets in Luzon to send a message that their influence is spreading in places far from their strongholds, security officials said.

President Rodrigo Duterte's spokesman Salvador Panelo on Tuesday (Aug 6) confirmed that security forces in Luzon were on heightened alert to thwart such attacks.

According to Mr Banlaoi, a third Sri Lankan, Anarkalie Dulara Palliyaguruge, was also involved in these plots. "Anarkalie is the financier," he said.

The Sri Lankan has so far been unable to sneak into the Philippines.

Besides the Sri Lankans, an Egyptian couple, both veterans of the fighting in Syria and Afghanistan, were also reported to be in the Philippines to train a younger crop of militants on suicide bombing.

Some 200 Indonesians had also made their way to jungle camps of ISIS-linked groups in war-torn Mindanao island.

"There are dangers ahead. I share the apprehensions of President Duterte," said Mr Banlaoi.

The President on Monday (Aug 5) voiced concerns over possible ISIS-inspired attacks in Luzon.

"I have ISIS, and this is what I am most afraid of," he said in a speech. "I am praying, really praying, kneeling before God, to spare us the kind of brutality and cruelty (ISIS brings) because it will really be bloody, bloody as it can be."

Mr Duterte said he was looking at recruiting thousands more to augment the military's special forces units.

"We are facing so many fronts. I need more soldiers," he added.