Supporters of a Muslim rebel chief who accepted a peace deal with the Philippine government five years ago, attacked a southern town today, army officials said.
It is an apparent bid to postpone elections Mr Nur Misuari could lose, the army said.
Military officials said Mr Misuari's followers attacked an army outpost on Jolo Island, 960 kilometres south of Manila, early this morning and then began shelling the main town, also called Jolo.
The brigade headquarters and the airport there were under mortar attack, but there was no immediate word of casualties.
Some soldiers, formerly in the Moro National Liberation Front (MNLF) of Nur Misuari and inducted into the military after the 1996 accord, mutinied and joined MNLF fighters in the attacks, the army said.
There were no details on how many guerrillas were involved in the attacks, which came one day after southern military commander Lieut Gen Roy Cimatu warned Mr Misuari could take up arms to oppose the holding of local elections on November 26th.
Mr Misuari is up for re-election as governor of the Autonomous Region of Muslim Mindanao, but administration officials in Manila have accused him of mismanaging the area and have indicated they will support another MNLF candidate.
"This is all the handiwork of Misuari for his personal vested interests," military spokesman Col Danilo said.