MANILA (UPDATE 2) — At least 4 people were killed and 9 were injured after an explosion rocked Mindanao State University (MSU) in Marawi City, police said Sunday.

The blast happened at the university's gymnasium where the victims were attending a mass.

More than 40 people were brought to government hospital Amai Pakpak Medical Center following the deadly explosion. Six of them were inside the operating room.

Motive yet to be determined

Lanao del Sur Gov. Mamintal Alonto Adiong Jr., who has visited the gymnasium and has conferred with victims at a nearby hospital, condemned the blast.

“Here in my province, we uphold basic human rights, and that includes the right to religion. Terroristic attacks on educational institutions must also be condemned because these are places that promote the culture of peace and mold our youth to be the future shapers of this country,” he said.

Adiong called on the security sector to find the perpetrators and sent his condolences to the victims of the explosion.

“We will make sure justice will be served,” he also said.

Lanao del Sur 1st District Rep. Zia Alonto Adiong, the governor's brother, said four people are confirmed to have died.

"I express the highest condemnation for these perpetrators, these murderers who targeted innocents in prayer," he said.

"There is no room in Marawi, in Lanao del Sur, or in the entire Philippines for them."

Police BGen Allan Nobleza, director of Police Regional Office-Bangsamoro Autonomous Region in Muslim Mindanao, said authorities have yet to determine motive or identify what explosive was used.

"Tinitingnan pa natin kung ito ba ay may koneksyon sa mga operations na inilunsad ng puwersa ng kasundaluhan at kapulisan sa BARMM," he also said.

(We are trying to find out if this is related to operations that the military and police have launched in BARMM.)

MSU deeply saddened, appalled by blast

The MSU said it was "deeply saddened" and "appalled" by the violence.

"We unequivocally condemn in the strongest possible terms this senseless and horrific act," it said in a statement.

The university assured that it would provide support to the victims of the blast, saying its immediate priority was to "ensure the safety and well-being of all constituents, particularly our Christian community."

"We are aware of the heightened sensitivities and concerns that arise from such a tragic event, and we want to assure everyone that we are taking every measure possible to protect our students, faculty, and staff," it also said.

The explosion prompted the university to suspend classes "until further notice," adding that it had deployed additional security personnel to safeguard the campus.

"We are working closely with the local government units and law enforcement authorities to investigate this incident and bring the perpetrators to justice," the university also said.

More details to follow.

—Reports from Merlyn Manos, Lerio Bompat and Raya Capulong, ABS-CBN News