At least four people were killed and over 50 others injured in an explosion inside the gym of a university during a Catholic mass in the southern Philippine province of Lanao del Sur on Sunday morning, local authorities said.

Philippine President Ferdinand Romualdez Marcos Jr condemned the bombing attack, saying the act was perpetrated by "foreign terrorists."

"I condemn in the strongest possible terms the senseless and most heinous acts perpetrated by foreign terrorists," Marcos said in a statement. "Extremists who wield violence against the innocent will always be regarded as enemies to our society."

The country's Defense Secretary Gilberto Teodoro also told media at a press conference there were "strong indications of a foreign element" in the bombing but refused to elaborate so as not to compromise the ongoing investigation.

(With input from Reuters)