Philippine forces were on high alert on Sunday after a bomb killed four people and wounded several during a Catholic Mass in a university gymnasium in the south of the country, an attack the authorities called Islamist terrorism.
"I condemn in the strongest possible terms the senseless and most heinous acts perpetrated by foreign terrorists," said President Ferdinand Marcos Jr. "Extremists who wield violence against the innocent will always be regarded as enemies to our society."
The blast in Marawi, a city besieged by pro-Islamic State terrorists for five months in 2017, followed the killing of 11 combatants in a military operation on Friday in Maguindanao del Sur some 200 km (125 miles) away.
Urging calm, Marcos posted on the social media platform X that he had instructed the national police and armed forces "to ensure the protection and safety of civilians and the security of affected and vulnerable communities."
"Rest assured we will bring the perpetrators of this ruthless act to justice."