Soldiers ambushed while hunting kidnapped Italian priest on Basilan island.
Lieutenant General Eugenio Cedo, a regional military commander, said they were unable to “assess properly the strength of the enemy during the assault”.
The military is still looking for one of the group’s commanders, Isnilon Hapilon, wanted by both the US and Philippine governments for alleged kidnappings and bombings.
General Hermogenes Esperon, the military chief of staff, said Hapilon was among those being hunted by troops in Basilan.
It remains unclear if Hapilon was involved in Saturday’s incident.
“We are making a promise to make the province unfit for those who want to rule it with arms,” Esperon said.
“The Muslims of the Philippines want autonomy and equal rights – democracy has failed them so they have taken up arms”
Shafiq, Dhaka, Bangladesh
On nearby Jolo island, troops raided a suspected Abu Sayyaf safe house early on Sunday, a military official said.
Army Major General Ruben Rafael said 19 men, women and children were taken into custody, and four M-16 rifles and ammunition were seized.
He said 14 of them were released but investigators were trying to ascertain if the five men still in custody were Abu Sayyaf fighters.
The MILF has admitted ambushing a number of marines in July after they entered their territory unannounced but denied being involved in the beheading.