Last month, in a deadly clash in Lanao del Norte province, Islamist militants affiliated with the Middle East-based Islamic State of Iraq and Syria (ISIS) killed six commandos from the Philippine Army’s elite Scout Ranger battalion.

Three local Islamist militants were also killed.

The gunbattle in Munai town was a grim reminder that the remnants of the violent Daulah Islamiyah-Maute group remained a real security threat in the southern Philippines.

From the late 1960s, Muslim separarists belonging to the Moro National Liberation Fromt (MNLF) and the more fundamentalist Moro Liberation Front (MILF) created security problems in Mindanao, Basilan, Sulu, and Tawi-tawi.

But the government was successful in negotiating peace agreements with these rebel groups.

However, returning mujahideens from the Middle East continued the struggle for self-determination, forming smaller and more violent groups with links to Southeast Asian and Middle East Islamist militants organizations.

By the early 2000s, Mindanao had become a popular destination for many foreign Islamist militants seeking training, exposure and experience in guerrilla warfare.

In 2017, these smaller groups – the Abu Sayyaf from Sulu and Basilan, the Bangsamoro Islamic Freedom Figthets from Maguindanao, and the Maute group from Lanao del Sur — banded together to seize control and occupy Marawi City in Lanao del Sur.

It was unimaginable for rival ethnic Muslim militants to join forces and rally under the Islamic State banner.

It took five months before the military could regain control of the country’s only Islamic City, leaving it in ruins and displacing tens of thousands of residents.

After the Marawi conflict, the military thought it had decimated the Islamist militants after their leaders – Isnilon Hapilon and the Maute brothers, Omar and Abdullah – were killed.

But lesser-known militant leaders soon emerged and continued the struggle to create an independent, separate, and free Islamic state.

The nation was shocked when the Daulah Islamiyah-Maute group detonated last December an improvised explosive device during a Roman Catholic Mass inside a gymnasium at the campus of Mindanao State University in Marawi City, killing four people and wounding 50 others.

It was a wakeup call. Threats from small and violent Islamist militants had not been totally defeated.

The Philippines has to revisit its move to shift to territorial defense from internal security operations as terrorism remains a concern in the south.

Mindanao could still be a sanctuary and training ground for foreign Islamist militants. Dozens of Southeast Asian fighters had returned from Afghanistan, Iraq, and Syria to Indonesia, Malaysia and the Philippines.

Mindanao remains attractive to these returning Islamist militants because of the unstable security situation.

Despite peace agreements with both the MNLF and the MILF, the situation remains shaky as the government struggles to fulfill its financial obligations.

Within the former rebel movement, there has been a constant struggle between the elder leaders who are tired of fighting and the younger, more radical emerging leaders who demand a free and separate Islamic state.

Next year’s elections at the Bangsamoro Autonomous Region in Muslim Mindanao (BARMM) could also be problematic if the MILF leadership loses control over the region.

The December attack at MSU could demonstrate a possible surge in Islamist militants’ activity in the south.

There are other factors that may fuel the rise in terrorist attacks in the south – the battle to replace Abu Zacaria as the emir or leader of the Islamic State’s East Asia Wilayah.

Faharudin Hadji Benito Satar or Abu Zacaria was killed in a military raid in June last year in Marawi City.

Some officials, led by Vice President Sara Duterte-Carpio, have also objected to bringing 50,000 Afghan refugees to the country because they could pose as a security threat.

The Philippines should not dismiss the potential threats from smaller Islamist militants.

The conditions on the ground remained very volatile and it could suddenly flare up with the rising conflicts around the world, like Ukraine and the Gaza Strip.

Mindanao will become an attractive training ground, again, for Islamist militants to be deployed in hotspots around the globe as the Philippines has been paying more attention to the disputed South China Sea, away from internal security threats.

Perhaps, the Philippines could also review the deployment of small US Special Forces contingent in Mindanao.

After the September 11 attacks, the US opened a second front on its global war on terror in the southern Philippines, sending 2,000 soldiers and building coastal radar stations to monitor Islamist militants movements and activities along the borders of Indonesia, Malaysia and the Philippines.

Lately, Washington has reduced the numbers to 100 to 200 troops as the threats have subsided with the death of Osama bin Laden and the defeat of the Islamic State.

The presence of some local and foreign Islamist militants in Mindanao could be a good cover for the US continued deployment.

However, the Mamasapano incident in 2015, the Marawi conflict in 2017, and the latest bomb attack at MSU put a big question mark on Washington’s role in preventing such events.

The US had some roles in Mamasapano and in Marawi. The Philippines has to review how beneficial the US presence in Mindanao because Washington may have shifted its focus to countering China’s growing influence in the region rather than fighting Islamist militancy.