A team of soldiers with local election officials were on their way to return vote-counting machines to Margusan town in the mining region on Mindanao when New People's Army (NPA) rebels opened fire on them, Lt. Col. Ernesto Torres said.

"We lost four soldiers and two civilians, including an election officer, were killed in the attack," Torres said, adding a dozen others, including nine soldiers, were wounded.

Torres said NPA rebels were behind the attack, saying it was "a grave attempt to jeopardize the country's democracy.”

On Monday, when voting took place, bombs, grenades and shootings killed nine people and wounded 12, which security officials described as one of the country's most peaceful elections.