Another 42 people sustained injuries, according to Jenny Tamano, the spokesperson for the provincial government.
The incident happened when several worshippers had gathered for a morning mass in a gymnasium at the state-run Marawi State University in Marawi city on Sunday morning.
The blast caused panic among dozens of people who rushed to leave the victims bloodied and sprawled on the ground, said Taha Mandangan, security chief of the sprawling state-run campus.
“This is clearly an act of terrorism. It’s not a simple feud between two people. A bomb will kill everybody around,” Mr Mandangan told the Associated Press.
Marawi State University said it was “deeply saddened and appalled” by the “senseless and horrific” violence.
“Violence has no place in a civilised society, and it is particularly abhorrent in an institution of higher learning like MSU,” it said.
“We stand in solidarity with our Christian community and all those affected by this tragedy.”
The blast ripped through the predominantly Muslim city in the southern Philippines which had previously come under attack for five months from Islamic militants aligned with the Islamic State group in 2017, leaving more than 1,100 killed.
Lanao del Sur governor, Mamintal Adiong Jr who arrived at the site of the explosion condemned the “violent bombing incident”.
“To the families of those whose lives were lost in this senseless act of violence and terrorism, please accept our deepest condolences and sympathies. We will make sure justice will be served,” Mr Adiong said in a statement.
Earlier, it was reported that three people were killed and nine were injured in the explosion. Later, Lanao del Sur provincial government spokesperson released an update regarding the casualty count, according to Rappler.
President Ferdinand Marcos condemned the incident, saying it was conducted by foreign terrorists.
“I condemn in the strongest possible terms the senseless and most heinous acts perpetrated by foreign terrorists upon the Mindanao State University (MSU) and Marawi communities early this Sunday morning,” he said.
Military and law enforcement immediately cordoned off the area, launching a preliminary inquiry and reviewing surveillance footage to identify those responsible for the attack. Security checkpoints were established throughout the city.
The explosion happened when several people, including several students who were at the gym, had gathered for a Mass at around 7am, brigadier general Allan Cruz Nobleza, police director in the Bangsamoro Autonomous Region in Muslim Mindanao (BARMM) said.
He said investigators were assessing whether a homemade bomb or a grenade was used in the attack.
The explosion occurred just two days after the forces conducted a surgical strike, resulting in the death of 11 suspected members of the terrorist group Dawlah Islamiyah and their leader near Datu Hoffer town in southern Maguindanao province.
Mr Nobleza stated that they are also investigating whether the blast is linked to the military offensive backed by airstrikes and artillery fires on Friday.
LOOK | NEWS UPDATE: Lanao del Sur Governor Mamintal Adiong, Jr. speaks with authorities as he checks the MSU gym in Marawi City where an explosion took place during a religious Mass morning on December 3, 2023
| Photo courtesy: Provincial Government of Lanao del Sur Facebook pic.twitter.com/GEkiBU6NS2
— GMA Regional TV News (@GMARTVNews) December 3, 2023
He mentioned that the militants killed in the military operation belonged to Dawlah Islamiyah, an armed group that had aligned itself with the Islamic State group and continues to have a presence in Lanao del Sur province, where Marawi City is located
The mosque-studded southern Philippines, the homeland of minority Muslims in the predominantly Roman Catholic nation, has remained at the centre of the decades-old separatist rebellion.
In 2014, the largest armed insurgent group, the Moro Islamic Liberation Front signed a peace deal with the government, easing the tensions in the area.
However, a number of smaller armed groups have rejected the peace pact and continued their offensive with bombings and attacks.