The UN and the Philippine military both condemned Wednesday's attack in Basilan island, which came more than a decade after the Moro Islamic Liberation Front (MILF) signed a peace agreement with Manila.

The 2014 peace deal ended a decades-long armed campaign, initially for a separate state and later Muslim self-rule in Asia's bastion of Catholicism, but the decommissioning of weapons has yet to be completed.

A military statement said the soldiers were "fired upon by unidentified armed personalities", triggering a firefight that left two soldiers dead and 12 others wounded.

The soldiers' commander, Brigadier General Alvin Luzon, said Thursday that MILF gunmen were responsible for the attack, and that the UN visit to the former rebel stronghold was aborted.

UN resident coordinator Gustavo Gonzalez "strongly" condemned the ambush, which he said occured when Philippine troops were escorting a team from United Nations Development Programme (UNDP) "for community engagement in the area".

"This was the first such incident involving a United Nations team since the implementation of the peace process," Gonzalez said in a statement, adding "we will stay and deliver" on the UN commitment to support peacebuilding efforts in the southern Philippines.

The peace deal led to the creation of a self-rule area in the Muslim-populated region, with an elected parliament and chief minister, former MILF chief Ahod Ebrahim.

Ebrahim said in a statement sent to AFP that the regional Bangsamoro government -- which includes the island province of Basilan -- was "deeply saddened by the unfortunate encounter" between the army and the MILF forces.

He urged all parties to "remain calm as we work towards addressing this incident through appropriate channels", while stressing the regional government "remains steadfast in its commitment to the full implementation" of the peace treaty.

Philippine Army commander Lieutenant General Roy Galido condemned the attack and said his forces are "working closely with local government units and law enforcement agencies to ensure that the perpetrators of this treacherous act face the full consequences of their actions".