“In Davao I used to do it personally. Just to show to the guys (police) that if I can do it why can’t you,” Duterte said in his speech at the presidential palace.

“And I’d go around in Davao with a motorcycle, with a big bike around, and I would just patrol the streets, looking for trouble also. I was really looking for a confrontation so I could kill.”

Late on Wednesday,the Philippine justice secretary said Duterte often exaggerated about the killings of criminals he supposedly carried out to send a chilling warning to lawbreakers. Vitaliano Aguirre II said that Duterte may have been resorting to hyperbole when he suggested that he used to go around Davao looking for criminals to kill.

“If they say that I am afraid to stop (the campaign) because of the human rights and guys from including Obama: Sorry, I am not about to do that,” he said in English.

Rights groups have previously accused Duterte of running vigilante death squads in Davao that killed more than 1,000 suspected criminals.

Duterte has variously denied and acknowledged his involvement in the death squads.

Similarly, Duterte as president has called on ordinary Filipinos as well as security forces to kill drug users and traffickers. But he has also said that he and his security forces would not break the law.

Watch: Duterte ‘s war on drugs

In October, Duterte compared himself to Adolf Hitler and said he would be “happy to slaughter” three million drug addicts.

Since his election, police have reported killing 2,086 people in anti-drug operations. More than 3,000 others have been killed in unexplained circumstances, according to official figures.

Watch: Duterte shoot pistol at a firing range

Often masked assailants break into shanty homes and kill people who have been tagged as drug traffickers or drug users. Rights groups have warned of a breakdown in the rule of law with police and hired assassins operating with complete impunity.

Duterte has insisted that police are only killing in self-defence and gangsters are murdering the other victims.

But he has also said he will not allow any police to go to jail if they are found guilty of murder in prosecuting his crime war.

Duterte also told the business leaders that he had no fear of being removed from power or assassinated because of opposition to the rising death toll in his anti-drugs campaign.

“Oust me - good; assassinate me - better; I have this migraine every day,” he said. “I have a lot of issues with my spine. What I have is really Buerger’s disease. It’s an acquired thing that you get from smoking, because of nicotine.”

Doctors had advised surgery on his spine, he said, but his wife, a nurse who used to work in the United States, did not agree because “a lot of operations for the spine went wrong”.

He added: “If you guys see me always in a sad mood, I am actually pushing a nerve here to relieve the pain,” and touched the right side of his face.

Presidential spokesman Ernesto Abella said the health issues had not affected Duterte’s work, dismissing the remarks as “Nothing serious”. Duterte no longer smokes or drinks alcohol.

Duterte, who will be 77 at the end of his six-year term in 2022, is the oldest person to be elected president in the Philippines since the post-war period.

Additional reporting by Reuters and Associated Press