At least four people died Sunday in the aftermath of an explosion at Mindanao State University in Marawi City, Philippines, according to reports.

The blast occurred at a morning Mass inside a gymnasium at the state-run university. Another 42 people were injured, according to government spokeswoman Jenny Tamano.

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“This is clearly an act of terrorism," campus security chief Taha Mandangan told the Associated Press. "It’s not a simple feud between two people. A bomb will kill everybody around."

Worshippers had gathered for the First Sunday of Advent, the traditional Catholic preparation for Christmas.