The government wrapped up peace talks with the nation's biggest Muslim rebel group on Saturday, then quickly deployed the military against a hardline splinter faction called the Bangsamoro Islamic Freedom Fighters (BIFF).
"The armed forces... (are) going on these operations to prevent lawless activities from inflicting harm on our population, and to seriously degrade their abilities to again act as (peace) spoilers," Aquino told reporters in Manila.
About 150,000 people have been killed in the conflict.
Under the planned peace accord, the MILF will have control over an autonomous Muslim region in the southern Philippines. Aquino is aiming for the peace plan to be finalised before he steps down in mid-2016.
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The BIFF is a breakaway group of a few hundred militants which believes the 12,000-strong MILF has compromised too much in the peace process. It has carried out many deadly attacks in recent years to try to derail peace efforts.
One soldier was also killed and seven others wounded, Hermoso told reporters, as he described strong but fading resistance from the small number of BIFF fighters against about 1,500 soldiers.
"They (rebels) set off improvised explosive devices and directed mortar fire on our troops. But they have splintered into smaller groups and our troops are now clearing these areas," Hermoso said.
Three civilians were also hurt in the violence, including two from a Tuesday bomb blast near a marketplace that the military blamed on the BIFF, according to Hermoso.