At least three people were killed and others injured Sunday morning in an explosion during a Mass held in a university gymnasium in the southern Philippines.

Authorities are investigating whether pro-Islamic State militants were responsible for the blast, which set off a panic on the campus of Mindanao State University in Marawi on the island of Mindanao. The province, located on the borders of Malaysia and Indonesia, is home to several Islamist militant groups fighting against the Philippine government.

“This is clearly an act of terrorism. It’s not a simple feud between two people. A bomb will kill everybody around,” Taha Mandangan, the university’s security chief, told The Associated Press. The explosion left the victims bloodied and sprawled on the ground, he said.

Reuters and other media outlets reported that three were killed and nine wounded. A government official later said four had died and scores were injured.

The official, Carlito Galvez Jr., a retired Philippine Army general serving as a presidential adviser to Philippine President Ferdinand Marcos Jr. on the peace process, issued a statement condemning the violence.

“This horrendous attack, which happened during a Mass and the Mindinao Week of Peace, shows the ruthless methods these lawless elements will utilize to sow fear, anger, and animosity among our people. We will not allow this to happen,” Galvez said. “Such a barbaric act has no room in a human civilized and peaceful society.”

Mindanao State University issued a statement on Facebook saying it is “deeply saddened and appalled by the act of violence that occurred during a religious gathering.” The university said it was suspending classes until further notice.