President Rodrigo Duterte has asked police and the military to reassess their anti-drug operations following the conviction of three cops for killing a teenager in Caloocan City last year.

This as Duterte categorically said he would not pardon the three members of the Philippine National Police who were convicted for murdering Kian delos Santos.

"No, of course not, maybe one million years from now," he told reporters on Monday in Malacanang.

Duterte said his promise to pardon the police and soldiers was premised on the commission of some acts while doing their job.

"Look, what I said was I will defend to death my soldiers and my policemen if they commit some acts which could be considered criminal but done in the performance of their duties," he said.

He said his order to government forces to kill criminals was if, in the performance of their duty, their life would be in danger.

Duterte wondered why police have to kill illegally.

"That's why police, military, kindly reassess. Lately, there were lots of police who have been caught. Why do you have to kill them (victims) illegally? You can always corner them, found out if they are - or they have committed the shabu, act of trafficking...and if he resists arrest violently, you are free to kill them," he said in a speech Monday night.

Duterte said he was at a loss how to explain to policemen and military his order.

But despite his order to review the anti-drug operations, Duterte said there is no let up in the campaign against illegal drugs.

"There will never be a let-up in the campaign against drugs and the killing will continue for as long as there are people who would resist arrest and fight it out. That is my order and it will be until I leave the premises of this place. It will be their policy. I don’t care about tomorrow. I can go to prison for my countrymen....I'm old," the 73-year old Duterte said.

Nearly 5,000 people have been killed in the war on drugs since Duterte assumed office in June 2016. Celerina Monte/DMS