Officials said the MILF missed the target, but damaged nearby houses in Barangay Salunayan.
The attack came less than 24 hours after the joint ceasefire committee agreed on the repositioning of troops and MILF rebels away from Barangays Kadigasan and Lumupog in Midsayap.
Midsayap Mayor Romeo Arana said soldiers had left three barangays at the center of the conflict, and that he was overseeing the return of about 4,500 residents who had fled the fighting.
Military officials said troops withdrew from several Midsayap barangays Wednesday to avoid escalation of violence with the MILF.
Superintendent Chino Mamburam, Midysayap police chief, said the blasts roused residents from sleep, but that there was no immediate sign they were about to flee, Lt. Col. Julieto Ando, Army 6th Infantry Division spokesman, said the guerrillas apparently wanted to avenge the deaths of 17 rebels who were killed Monday in fierce fighting in Midsayap, triggered by rebel allegations that troops were encroaching on their strongholds.
Eid Kabalu, MILF spokesman, said the guerrillas launched the mortar attack because Army troops continued to move into guerrilla positions despite efforts by a government-rebel ceasefire committee to contain days of sporadic fighting.
"We’re being pushed against the wall," he said. "We have no recourse but to fight back. The fighting will not end unless army troops withdraw from rebel positions."