A Philippine military official says up to 20 Muslim militants are believed to have been killed in three days of sporadic clashes that also left three soldiers dead in the country's south.

Military spokesman Brig. Gen. Restituto Padilla said the fighting broke out when about 40 militants from a still unspecified group opened fire late Saturday on an army camp in Butig town in Lanao del Sur province. Soldiers defended the camp in on-and-off clashes.

Padilla said the military deployed additional troops, bomber planes, helicopter gunships and artillery to the area.

The attackers may have come from a group affiliated with an Indonesian terror suspect who was killed in the region in 2012.