Philippine President Ferdinand Marcos Jr condemned a deadly bombing on Sunday, blaming “foreign terrorists”, as police and the military strengthened security in the country’s south and around the capital, Manila.

At least four people were killed and at least 50 injured after a bomb exploded during a morning Catholic Mass in a university gymnasium in Marawi, a city in the south of the country besieged by Islamist militants for five months in 2017.

“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.”