The IED exploded at Oval Plaza, General Santos City, South Cotabato at around 9:10 p.m. Thursday, said Army spokesperson Lieutenant Colonel Romeo Brawner Jr. The victims were taken to different hospitals in General Santos City for medical treatment.
Meanwhile, the Philippine National Police (PNP) said that the explosion happened at around 9:20 p.m. and was caused by a hand grenade and not an IED.
Police also said that the explosion had injured 23 persons.
Both the PNP and military said that they have not identified any suspects behind the bombing as investigations are still ongoing.
Security forces have been on heightened alert for possible attacks by Muslim separatist Moro Islamic Liberation Front (MILF) rebels who have been locked in intense battles with troops since August.
A grenade attack Tuesday on a police outpost in General Santos wounded a policeman and two other people.
The same day, a suspected militant transporting an improvised explosive device was killed when it went off at a police checkpoint near the town of Esperanza, also on Mindanao island.