Four separatist fighters were killed and three pro-government militiamen were wounded in the fighting around Mamasapano town on Mindanao island, on Wednesday, which the military alleged was sparked by a Moro Islamic Liberation Front (MILF) guerrilla attack on an army outpost.
The fighting shattered a two-year-old truce that was being observed by more than 60 international military monitors from Brunei and Malaysia.
MILF spokesman Eid Kabalu blamed the military for starting the violence, adding that fighting had spread to several nearby villages.
"Fighting is still raging at least in two villages now, Tuca and Lupok, and we are awaiting reports from our commanders in the field on the extent of the battle. Troops attacked our positions in Mamasapano town," Kabalu said.
The military said fighting was triggered when 30-40 members of the MILF attacked a residential area and three army detachments.
Regional military spokesman Colonel Franklin del Prado said rebel forces attacked a military post in Tuca village without provocation before dawn.
"We still don't have reports of casualties and fighting is going on," he said.
Alexander Yano (2-L) says the
ceasefire group will intervene
Brigadier General Alexander Yano, chairman of a joint committee overseeing the ceasefire, said committee members along with representatives of the MILF were proceeding to the area to look into the incident.
"We will let the (ceasefire committee) handle the matter first," Yano said.
However, he added that the military was checking into reports that the MILF was massing its forces in the area.
Manila hopes to start peace talks with the MILF after the Muslim month of Ramadan ends later this month.
Malaysia has agreed to host the talks.