Lanao del Sur Gov. Mamintal Alonto Adiong Jr. on Sunday said an improvised explosive device was behind the explosion at the gymnasium of Mindanao State University (MSU) in Marawi City.

Adiong said at least 3 people were killed instantly in the explosion while a fourth victim died at Amai Pakpak Medical Center.

Some 40 people were brought to government hospital following the deadly explosion.

"'Yung iba na daplis lang ang sugat inilipat na natin sa Mindanao State University infirminary, 'yung iba naman na kaunti lang ang sugat ay nakauwi na rin," he said.

He urged the public not to speculate on who was behind the 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.