The Islamic State terror group (ISIS) has claimed responsibility for the lethal bombing of a Catholic Mass in the Philippines this weekend as worshipers celebrated the first Sunday of Advent.

The bombing of morning worship at Mindanao State University’s gymnasium in Marawi, the country’s largest Muslim city, killed at least four people and left more than 50 others wounded.

The Islamic State said in a statement on its Telegram channels that “soldiers of the caliphate detonated an explosive device on a large gathering of Christians… in the city of Marawi.”

Regional police Chief Allan Nobleza said that the blast may have been a revenge bombing after a Philippine military airstrike on Friday killed 11 Islamist militants from the Dawlah Islamiyah-Philippines organization in Mindanao.

Nobleza also said that Philippine police have identified at least two suspects in the bombing.

We have persons of interest, “but the investigation is still ongoing,” Nobleza said. “In order not to preempt the investigation, we will not divulge the names.”

Officials from Mindanao State University condemned “the act of violence,” saying the school stands “in solidarity with our Christian community and all those affected by this tragedy.”

Army Major General Gabriel Viray III defined the attack at the Mindanao State University as “a terror act,” noting that security forces are on “heightened alert” as they try to determine the motive and identify the perpetrators of the attack.

Pope Francis sent a telegram saying he was “deeply saddened” by news of the attack and assuring his “spiritual closeness” to all affected by the bombing.

The pope said he was commending the souls of those who died to “almighty God’s loving mercy” while imploring “the divine gifts of healing and consolation upon the injured and bereaved.”

Francis also pledged prayers that “Christ the Prince of Peace will grant to all the strength to turn from violence and overcome every evil with good.”

Thomas D. Williams is Breitbart Rome Bureau Chief and author of The Coming Christian Persecution.