On Sunday, an explosion at a Catholic mass in the Philippines killed at least four people and injured 50 others. Officials said the blast is believed to have been caused by a bomb after fragments of a 16-mm mortar were found a the scene.
The Islamic State group said its members had detonated the bomb on Telegram, Reuters reports.
According to NBC, the explosion occurred in a gymnasium at Mindanao State University in the city of Marawi, and Philippine President Ferdinand Marcos Jr. blamed "foreign terrorists" for the attack.
"I condemn in the strongest possible terms the senseless and most heinous acts perpetrated by foreign terrorists," he said in a statement. "Extremists who wield violence against the innocent will always be regarded as enemies to our society.”
Defense Secretary Gilberto Teodoro said there were "strong indications of a foreign element," and noted that law enforcement agents will "continue unabated" bringing perpetrators of "terrorist activity" to justice.
In 2017, Marawi was besieged by Islamic terrorists for five months, and there have been a series of military operations against pro-Islamic State organizations recently. Sunday, the military killed the leader of the radical Islamist Maute group, Lanao del Sur.
Armed Forces Cheif Romeo Brawner said at a news conference, “It is possible that what happened this morning was a retaliatory attack."
In a statement, presidential adviser Carlito Galvez said, "This horrendous attack, which happened during a Mass … shows the ruthless methods that these lawless elements will utilize to sow fear, anger and animosity among our people." he added, "We will not allow this to happen.”
In a statement reacting to Sunday's attack Mindanao State University said it is "deeply saddened and appalled by the act of violence that occurred during a religious gathering." The statement added, "We unequivocally condemn in the strongest possible terms this senseless and horrific act.”
The security chief of the campus, Taha Mandangan told the Associated Press, "This is clearly an act of terrorism. It’s not a simple feud between two people. A bomb will kill everybody around."
Police in the region were placed on high alert and tightened security "to prevent possible follow-up incidents."