"The Duterte administration is empowering vigilante killings," he added, citing Mr Duterte's calls for ordinary citizens to kill drug dealers and his vow to protect officers who get sued while pursuing his drug campaign.
A sniper shot Mayor Antonio Halili, who was on Mr Duterte's list of allegedly narcotics-linked officials, during a public ceremony at the city hall in nearby Tanauan last Monday. A day later motorcycle-riding gunmen killed Duterte ally Ferdinand Bote, the Mayor of the northern town of General Tinio.
However, neither Mr Bote nor Mr Lubigan, the Vice-Mayor killed last Saturday, had known drug links. No clear motive has emerged yet.
"Election-related violence usually ramps up a few months before an election," Human Rights Watch researcher Carlos Conde said, noting that polls were 10 months away.
"The difference here really is the way Duterte has threatened officials with death and then they are being killed one after the other. That's hardly coincidence," Mr Conde added.
According to a count by police, more than two dozen people were killed in "election-related violence" during campaigning for the May 2016 national elections.
At least 10 mayors including Mr Halili and Mr Bote, have been killed since Mr Duterte took office, while Mr Lubigan, a member of a political party allied with the President, was the fifth vice-mayor killed in that period.
Mr Duterte ran on a law-and-order platform that included promises to kill thousands of people involved in the drug trade, including officials. The authorities have acknowledged killing more than 4,200 drug suspects who resisted arrest, but rights groups say the actual figureis at least triple that and could amount to crimes against humanity.
National police chief Oscar Albayalde told reporters yesterday the authorities were looking into possible motives for the killings, while noting it was a well-established fact that deadly attacks against elected officials spike "before, during and after the elections" . President Duterte Already warn the Narco Politians last year to stop their illegal Drug trade or else "i will Order to Assassinate you by a Sniper"