Philippine President Rodrigo Duterte on Friday dared the United States' CIA spy agency to try and oust him, as he branded Western critics of his deadly crime war "animals" and vowed many more killings.

In two fiery speeches to mark his 100 days in office, Duterte repeatedly raised the prospect of local or foreign opponents seeking to remove him from power in an effort to stop the violence.

But he insisted he would not be intimidated and that his campaign against drugs, in which an average of more than 33 people a day are being killed, would not end.

"You want to oust me? You want to use the CIA? Go ahead," Duterte said in a speech in his southern home town of Davao city, referring to the Central Intelligence Agency, while railing against US President Barack Obama and other critics.

Last month Duterte accused the CIA of plotting to kill him, but gave no specifics.

Also on Friday he referred to a local newspaper columnist who warned a "People Power" movement could form to try and topple Duterte, using the term coined for the revolution that overthrew dictator Ferdinand Marcos in 1986.

"Be my guest. I don't give a shit," he said.

"I'll be ousted? Fine. (If so) it's part of my destiny. Destiny carries so many things. If I die, that's part of my destiny. Presidents get assassinated."

Duterte was elected in a landslide this year mainly on a pledge to eradicate illegal drugs in society by killing tens of thousands of people.

Since taking office on June 30, police have killed 1,523 people and 1,838 others have died in unexplained circumstances, according to official figures.

A poll released this week showed Filipinos overwhelmingly approved of Duterte's first 100 days as president.

But rights groups have warned extrajudicial killings are out of control, with shadowy assassins murdering drug addicts, traffickers, petty criminals and opponents of powerful figures.

Duterte insists police are only killing in self-defence and the unexplained deaths are mainly due to drug gangs suddenly fighting each other.

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Duterte fuelled international concerns last week when he said he was "happy to slaughter" three million drug addicts, as he likened his campaign to Nazi leader Adolf Hitler's efforts to exterminate Jews.

He later apologised for the Hitler reference, but said he was "emphatic" about wanting to kill millions of addicts.

On Friday, Duterte again promised there would be no let-up.

"The drug campaign will not end. It will result in so many deaths and I do not apologise for it," he said in Davao.

In a barrage of separate tirades against his Western critics, Duterte told them not to think they were smarter than him and he would be prepared with many counter questions if they interrogated him.

"If they are unable to answer, son of a whore, go home, you animal. I will kick you now. Do not piss me off. It cannot be that they are brighter than me, believe me," he said.