"I might go down in history as the butcher. It's up to you," Mr Duterte told 1635 town and city mayors he summoned to the presidential palace.

"I will ask the chief of police to shoot you," he said.

Antonio Halili, the mayor of Tanauan City, near Manila, said that during the meeting Mr Duterte fumed about drugs destroying "the moral fabric of society".

"It's a very stern warning to those who are involved in drugs, that you should stop," said Mr Halili, who shames drugs suspects by parading them in his own province.

Mr Duterte's comments send a clear signal to police and the military they still have impunity to target drugs suspects, including mayors, in his crackdown that has been widely condemned around the world, including by the United Nations.

Mr Duterte defended police who controversially shot dead Rolando Espinosa, a mayor on the island of Leyte last November, while he was in a jail cell.

"He was killed in a very questionable way, but I don't care….the policemen said he resisted arrest. Then I will stick with the story of the arrest because they are under me," he said.

Mr Duterte, the former mayor of southern Davao City, was swept into office in July promising to eradicate the drugs menace within the first six months of his presidency.

He now admits he under-estimated the problem, claiming there are four million drugs addicts in the predominantly Catholic nation of 100 million people.

While Mr Duterte's popularity remains high, a December Social Weather Stations' survey found that 78 per cent of respondents expressed worry about becoming victims of an extra-judicial killing and 94 per cent said it is important that drugs suspects be captured alive.

More than 4000 of those killed were targeted in vigilante-style assassinations.

However no suspects have been arrested and charged in court.

Many of the assailants are believed to be police.

More than 2000 of the victims were killed by police who have justified the slaughter by claiming all of them chose to fight it out with law enforcers.

Bystanding victims have included children as young as five.

One commentator in Manila pointed out that if killings continue at the same rate at the end of Mr Duterte's first year in office four times more people will have been killed than during the darkest nine years of the Marcos dictatorship, from 1972 to 1981.

The late Ferdinand Marcos, his family and top cronies were forced into exile by a popular uprising in 1986.

Meanwhile, Rex Tillerson, US President-elect Donald Trump's nominee for Secretary of State, has refused to call the Philippines a human rights violator during a US Senate confirmation hearing, insisting he would need more information before he could make that assessment.

Criticism of the killings by the outgoing Obama administration prompted Mr Duterte to launch into expletive-laden tirades against the US, including telling Barack Obama to "go to hell" and calling him the "son of a whore."