An explosion during a Catholic mass in the southern Philippines has left at least four people dead.

The blast occurred on Sunday morning at a university gymnasium in the Muslim-majority city of Marawi on Mindanao Island.

The country's military and police said an unspecified number of injured people were taken to hospital.

Images taken at the scene show chairs, apparently made of plastic, scattered around on the charred floor.

No one has claimed responsibility. Authorities are investigating the incident as a suspected act of terrorism by Islamic militants.

President Ferdinand Marcos Jr. suggested that foreign terrorists could be behind the attack, which he condemned.

Marcos said, "Extremists who wield violence against the innocent will always be regarded as enemies to our society."

The Moro Islamic Liberation Front, the country's largest militant group, signed a peace agreement with the government in 2014 to end the fighting in Mindanao. The group is working toward the establishment of an autonomous government there in 2025.

But other armed groups oppose the move, and terror attacks have occurred frequently in the region.