Philippine forces were on high alert today after a bomb exploded that killed four people and injured several others during a Sunday Catholic service at a University of Mindanao gymnasium in the southern part of the country, an attack that authorities described as as Islamic terrorism.

“I condemn in the strongest possible terms the senseless and most heinous acts committed by foreign terrorists,” the president said. Ferdinand Marcos Jr. “Extremists who use violence against the innocent will always be seen as enemies of our society.”

The explosion in Marawi, a city besieged for five months in 2017 by jihadists who had pledged allegiance to the Islamic State group, followed a military operation Friday in Maguindanao del Sur, about 200 km away, in which 11 militants were killed.

Calling for calm, Marcos told Platform X that he had instructed the police and armed forces “to ensure the protection and safety of citizens and the safety of vulnerable and affected communities.”

“Rest assured that we will bring the perpetrators of this ruthless act to justice.”

The commander in chief Gabriel Viray III called the attack a “terrorist act”, speaking to reporters as explosive disposal experts were deployed to the scene. “We are currently on high alert and our troops remain on alert as we try to clarify the motive and identify the perpetrators to ascertain who is behind this.”

The University of Mindanao, in a message posted on its Facebook page, expressed “deep sadness and disgust at the act of violence that occurred during a religious gathering” and announced that classes are suspended until further notice.

Last Saturday, the Philippine military announced that it had killed 11 jihadists, including members of the Islamic State-affiliated Daulah Islamiya-Philippines group, in an operation the day before in Maguindanao del Sur.