Guerrillas from the New People's Army (NPA) opened fire on a government convoy on troubled Mindanao island yesterday, fatally wounding Mario Okinlay, according to a local military spokesman.
Okinlay was taken to hospital where he later died, while his attackers escaped, Army Major Christian Uy told AFP by telephone.
"The NPA sees Mayor Okinlay's good governance approach as an obstacle to their self-serving aims. Hence, they perpetrated this atrocity," Lieutenant-Colonel Romualdo Landingin said in a statement.
President Benigno Aquino had hoped to reach a peace deal with the insurgents before his six-year term ends in 2016, but planned peace talks have been hampered by rebel demands that detained comrades be freed.
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Parts of Mindanao are also plagued by Al-Qaeda-linked Muslim militants.
Okinlay was the mayor of Impasug-ong, a mountainous town of about 45,000 people located about 800 kilometres (500 miles) south of the capital Manila.
He and other officials of the town had just come from an overnight medical mission at a remote village when they were attacked, Landingin said.
Officials in the Philippines are often targeted by political rivals or communist insurgents.
Last month, gunmen shot dead a town mayor and two other people in a daylight roadside ambush in the rural town of Urbiztondo, north of Manila.