Duterte said Saturday he did not realize the severity of the problem until he became president. He's been accused of ordering or encouraging hundreds of killings of drug dealers and users since taking office in June.
"But the problem is ... I cannot kill them all ... even if I wanted to," he told reporters. "I did not have any idea that there were hundreds of thousands of people already in the drug business and what makes it worse is that they are operated now by people in government -- especially those elected positions."
His comments, which were made at a news conference on the release of a Norwegian hostage by a militant group
, came two days after Edgar Matobato, a self-described Duterte hit man, testified before a senate committee.
Matabato said he was part of a death squad to kill drug dealers
on orders from Duterte when the president was mayor of the city of Davao between 1988 and 2013.
Duterte's spokesman denied Duterte supports extajudicial killings. The president did tell police to shoot
if a criminal resisted arrest, and in a speech he also appeared to tell civilians to take the law into their own hands.
"If (a criminal) fights, and he fights to the death, you can kill him," he said. "Please feel free to call us, the police, or do it yourself if you have the gun ... you have my support."
Human Rights Watch said the nation needs an "independent" investigation into whether Duterte has had a role in extrajudicial killings. So far, the drug crackdown has made the president popular with many Philippines citizens,
although it also has opened him up to criticism that he and the police have gone too far.
Police Chief Ronald Dela Rosa told the senate committee investigating the killings there was no kill order, but people support the drug crackdown despite errors in judgment by police.
"We are only human... We admit we make mistakes, we are not perfect," he said.
The allegations along with Duterte's bombast, actions and temperament have already strained his relationship with the United States
, both key allies. He also threatened to pull the Philippines out of the United Nations
after criticisms about his drug crackdown
Duterte has referred to the US Ambassador to Manila,
Philip Goldberg, as "a gay son of a bitch." Duterte also recently derailed a meeting with President Barack Obama when he appeared to call Obama a "son of a whore" after the American president implied he would raise the issue of the drug crackdown at the meeting.
Duterte later apologized, saying he had been misunderstood.
Obama brushed aside the insult
, saying he understood Duterte, who has a reputation for vulgarity, was demonstrating his well-established vernacular.
"It seems as if this is a phrase he's used repeatedly, including directed at the pope and others," Obama said. "So, I think it seems to be just, you know, a habit."