Watchdogs have expressed concern Duterte's narcotics crackdown may be emboldening assailants.
PIC: President Rodrigo Duterte launched an anti-drug campaign after winning elections in mid-2016. (AFP)
A Philippine mayor on President Rodrigo Duterte's list of allegedly narcotics-linked officials was shot dead in his own office on Wednesday, police said.
Mariano Blanco, mayor of the southern town of Ronda, is the latest in a spate of local officials to be slain in recent months, some with and some without alleged links to the illegal drug trade.
The Philippines has a violent and often deadly political culture, but watchdogs have expressed concern Duterte's narcotics crackdown may be emboldening assailants.
Blanco, 59, was shot dead by unidentified gunmen after midnight in his office, the local police chief said.
"Witnesses said four armed persons alighted from a white van and entered the municipal hall... The mayor was there as he was sleeping in his office," Senior Inspector Jayr Palcon told AFP.
It was unclear why Blanco had decided to stay in his office overnight.
The mayor was pronounced dead at the hospital and the motive for the killing is under investigation.
Palcon said the mayor was on Duterte's so-called narco-list of officials involved in drugs, which was confirmed by a spokesman for the Philippines' Drug Enforcement Agency.
Blanco's killing comes nearly a year after the National Police Commission stripped him of control over the local police for allegedly being "engaged in illegal drug trade activities," the agency said.
Another recent high profile killing came in July when mayor Antonio Halili was shot by a sniper during a flag raising ceremony at the town hall in Tanauan, south of Manila.
Blanco and Halili are among at least six mayors or vice mayors killed in the Philippines since May.
Blanco's nephew and town vice mayor Jonah John Ungab was also shot dead by unidentified gunmen in February after attending a court hearing, police said.
The killings come as authorities are pursuing Duterte's deadly crackdown on narcotics.
Police say 4,410 alleged drug dealers or users have been killed as part of the anti-drug campaign that Duterte launched since winning elections in mid-2016.
Rights groups charge that the actual death toll is three times higher and that the police and shadowy vigilantes are murdering people even without proof they are linked to drugs.