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Manila - Motorcycle-borne gunmen on Tuesday assassinated a mayor in a town north of the Philippine capital, the second such killing of an official in two days, police said.

Ferdinand Bote, 57, became the 12th elected local official murdered since President Rodrigo Duterte unleashed a deadly anti-narcotics campaign after coming to power two years ago, although Bote was not linked to the drug trade.

He and his driver were leaving a government office in the capital of Nueva Ecija province when gunmen approached his sport utility vehicle and shot him dead, said Adrian Gabriel, the town's police chief.

"He was repeatedly shot with the use of a short firearm," police said in an initial report, but the driver escaped unhurt. Police retrieved at least 18 empty shells at the scene.

The government will spare no effort in getting to the bottom of the latest crime, said Harry Roque, a spokesman for Duterte.

"We assure everyone that we will discharge the state obligation for every murder," Roque said in a statement, promising a fair and thorough investigation by police to bring the perpetrators to justice.

On Monday, Antonio Halili, 72, who had gained prominence in 2016 for parading drug suspects in the streets of Tanauan, south of Manila, was hit by a bullet in the chest while attending a weekly flag-raising ceremony.

Duterte said the mayor may have had some drug involvement and his "walk of shame" campaign to parade suspects was a ploy to convince police he was not engaged in the illegal drug trade.

At Halili's wake, his daughter Angeline told reporters it was unfair to link her father to the drug trade, and said Duterte had been misinformed.

"I can't blame the president," she added. "If that's always what you hear from the same people that you talk to — and they keep telling you the same thing — it gets in your system to the point that you believe it, even though it's a lie."

Halili had been stripped of his supervisory powers over police in October 2017, due to a proliferation of illegal drugs in his city, amid allegations by the national police that he may have been involved. Halili had denied the allegations.

Police have killed more than 4 200 people in the anti-narcotics campaign since July 2016, with another 2 500 suspected drug suspects killed by unknown assailants over the same period.

Human rights advocates said the victims were executed by the police, who have denied the accusations, saying most of the killings were done in self-defence.