Manila (AFP) - Philippine President Rodrigo Duterte, who is waging a bloody war on crime, has justified the large-scale killing of drug users by suggesting the victims were not human.

Duterte, who has seen about two thousand people killed since he was elected in May, made the remarks late Friday as he shrugged off the United Nations' concerns over human rights in his country.

"Crime against humanity? In the first place, I’d like to be frank with you: are they humans? What is your definition of a human being?" he told soldiers while visiting an army camp, according to transcripts of his speech released afterwards.

"Human rights? Use it properly in the right context if you have the brains," he added.

"You cannot wage a war without killing," Duterte said, adding that many drug users were beyond rehabilitation.

His remarks came after various UN officials, including Secretary-General Ban Ki-moon in June condemned his apparent support for extra-judicial killings.

The UN special rapporteur on summary executions, Agnes Callamard, said earlier this month that his directives "amount to incitement to violence and killing, a crime under international law".

Duterte's comments come after his national police chief Ronald Dela Rosa on Friday urged drug users to kill their traffickers and burn their homes.

"Why don't you give them a visit, pour gasoline on their homes and set these on fire to register your anger," Dela Rosa said.

He later apologised for his remarks.

But Duterte defended Dela Rosa, saying "that's my style. He is following it".

Duterte also taunted the United Nations, saying "they want me to go prison? Do those idiots think I will be captured alive. My God, we will be together in hell."

Earlier this week, Dela Rosa told senators that over 750 people had been killed by police in anti-drug operations while more than a thousand had been slain by shadowy figures. Since then, even more people have been killed.

Duterte, 71, won May elections in a landslide on a promise to kill tens of thousands of suspected criminals to prevent the Philippines from becoming a narco-state.

He has vowed to protect policemen who may be charged as part of the campaign.