Manila, Dec. 3 -- An explosion occurred inside a gym of Mindanao State University in Marawi City, Lanao del Sur province in the southern Philippines on Sunday morning, killing at least four and injuring 50 others, local military and police said.

The blast occurred past 7 a.m. local time when students and teachers gathered for a Catholic mass inside the gym, according to local police.

Major General Gabriel Viray, the commander of the Army's 1st Infantry Division, said the deaths include three females and a male.

However, local media GMA Network put the death toll at 11, citing a local hospital source.

Police said the blast may have been caused by an improvised explosive device.

Philippine President Ferdinand Romualdez Marcos denounced t...