Philippine leader Rodrigo Duterte has promised in an exclusive interview with Al Jazeera to investigate extra-judicial killings as part of his war on drugs.

However, Duterte said in the interview broadcast on Thursday that his controversial campaign would go on against alleged criminals and drug-dealers. It is estimated to have led to the deaths of more than 3,000 people since June.

"You destroy my country - I'll kill you. And it's a legitimate thing," he said. "If you destroy our young children, I will kill you. That is a very correct statement. There is nothing wrong in trying to preserve the interests of the next generation."

READ MORE: Duterte tells Obama to 'go to hell'

But he said it was "bad" that children and innocent people have also been killed in the bloody crackdown.

Asked if he could promise there would be investigations into those cases, he replied: "Yes, of course, of course."

But he also suggested investigations might not lead to criminal liability.

"This is the law of my land. Here is a policeman, here is a gangster. He's armed with an M-16 [assault rifle], the gangster only with a pistol. But when they meet they exchange fire. With the policeman with his M-16 there's one burst and he hits 1,000 people there and they die. There's no criminal liability," said Duterte, nicknamed "the Punisher".

READ MORE: Duterte slams 'stupid' UN criticism of his war on drugs

He took his oath as president on June 30 and has vowed to keep his campaign promise of solving the country's illegal drug problem, saying, "I don't care about human rights, believe me."

The extrajudicial killings have been widely condemned by other world leaders and rights groups.

Duterte has been fighting off the criticism by using crude language towards them. He called the United Nations "stupid" and told US President Barack Obama to "go to hell".

Rodrigo Duterte: Guns, goons and the presidency - 101 East

Source: Al Jazeera News