Bomb threats circulated the night before the deadly explosion at the Dimaporo Gymnasium of Mindanao State University in Marawi City on Sunday, the Bangsamoro government said on Monday.
Bangsamoro Autonomous Region in Muslim Mindanao spokesperson Naguib Sinarimbo said text messages about a planned bombing started circulating on Saturday night without specifying the location.
"This really needs a thorough examination to pinpoint the true origin of this bombing," Sinarimbo said.
In 2017, Marawi, the capital city of Lanao del Sur, was besieged by militants affiliated with Isis, which caused around 1,000 casualties, becoming the Philippines' lengthiest urban conflict.
Nearly five years later, on 3 December 2023, an explosion occurred during a Catholic Mass at the MSU gym, resulting in the loss of at least four lives and injuries to at least 43 people.
Sinarimbo said that seven individuals were hospitalized with injuries that need surgery.
Pope prays for victims
"Based on reports we received from the emergency operation center of the Lanao del Sur provincial government and the incident command post at MSU, there are four confirmed fatalities," Sinarimbo said.
"Additionally, seven individuals still in the hospital require major surgeries," he added.
He said 43 other individuals received minor injuries, adding that the regional government would cover the hospital expenses.
At the Vatican, Pope Francis offered prayers for the victims of the bombing.
"I wish to assure my prayer for the victims of the attack that occurred this morning in the Philippines, where a bomb exploded during mass," he said in a post on X (formerly Twitter).
"I am close to the families and the people of Mindanao, who have already suffered so much," the pope added.