In a statement, Wesmincom spokesperson Col. Gerry Besana said three 60 mm mortar rounds exploded 200 meters from the Tanum Elementary School where a medical mission facilitated by the 6th Special Forces Battalion was ongoing.
The mortar rounds were estimated to have been fired 500 meters away from the school and was believed to be initiated by the Abu Sayyaf group to discourage residents from participating in the event.
"We strongly condemn this terroristic act resulting [in] the disruption of basic services delivery to the people," said Westmincom chief Lt. Gen. Arnel Dela Vega.
No casualty was reported among troops and participants in the medical mission.
The incident happened two weeks after a gunfight in the same town left 5 soldiers and 3 Abu Sayyaf bandits dead. The encounter happened after the military launched an operation to arrest Hajan Sawadjaan, an Abu Sayyaf leader.
Sawadjaan is believed to be involved in the twin bombings at the Jolo Cathedral during a mass on Jan. 27, where 22 were killed and more than 100 were hurt.